First you must decide what kind of a mod you will make, a totally new game based upon your own imagination or something based upon a movie, television series or maybe even a book. If you have an idea, search the internet for ideas and inspiration. You can start modding when you feel that you have a good idea of how it will look when it is done, I can tell you now that when it is finished it will not look like what you imagined, sometimes it looks even better and sometimes worse. But that is not important, as long as you learn how it is done.
Also, play the game a little so you know what each model does.
Got your idea? Good! Now we can start. Off course everyone is different but i like to start with the 3d models, you can search the internet until you find what you need or you can build them yourself, that takes some time I know but it will be worth it in the end. If you know how to build 3d models but you have no 3d program, then I would recommend Truespace, its easy to work with, looks great and is completely free.
I cant help you much with the building, but after that we get to the interesting part: putting the models into the game.
First you must copy then entire folder of "Starwars: Battle of Endor". You will find it in program files if you installed it to the standard folder which is: "C:\Program Files\STARWARS_TheBattleOfEndor_v21". Copy this folder to your desktop or "my documents". Then change the name of the folder to: "whatever you want to call your game".
Then change the name of the .exe file to: "whatever you called your game" and then make a shortcut to your desktop. Like that it will always be easy to test your game, by clicking on that shortcut.
By this time it should be noted that if you start experimenting on your own, it would be best to have a backup of what ever you have made so far.
Anyway, now open you 3D Program and open your 3d model then save it as a .x file also called "Direct X file". Then find the game folder in "my documents" or on your desktop or where you saved it and find the folder called "models" this folder is inside the game folder and cant be very hard to find. Then find these model files:
...these files are all the Xwing models in the game. Then, you might be wondering, what is the other file, xwing_far.x? This is the Xwing model you see when the model flies further away in the game, it basically means that it is less detailed than the normal Xwing model, this is to save virtual memory and to make the game run faster. If you look in that folder you will see that nearly all models have a "..._far.x" duplicate. Just make a simpler version of your model to use as the "_far.x" file. Then you must replace your models with the game models, so say that you are making a space shuttle game and you want the Xwings to be space shuttles, then you take your file, for example "shuttle.x", and you rename it to "xwing.x". After you have done that you just move it to the "models" folder and replace your "xwing.x" with the original "xwing.x" file.
You repeat this with all of your models and soon all the models are replaced, if you are not sure what all the .x files are, take a look at the list here below.
some of the 3d models in the folder "models":
awing.x = the awing model
bwing.x = the bwing model
bwing_far.x = less detailed bwing model
bwing_top_wing.x = is the top wing of a destroyed bwing (can be deleted without harm to the game)
bwing_wing.x = another wing of a destroyed bwing (can also be deleted)
bwing_bottom_wing.x = another wing of a destroyed bwing (can also be deleted)
xwing.x = the xwing model
xwing_far.x = less detailed xwing model
xwing_rightdown_leftup_wing.x = two wings of a destroyed xwing (can also be deleted)
xwing_rightdown_leftup_wing.x = two wings of a destroyed xwing (can also be deleted)
xwing_laser = is the "laser" model which you can change however you like. This model is used for all the allied ships. (if you want bullets you can build bullets, if you want a different laser you can build a different laser, it will work)
ywing_.x = the ywing model
ywing_far.x = less detailed ywing model
ywing_right_left_wing.x = the right and also left wing of an ywing
...ok, i think you get the picture, each model with "_far" behind it should be less detailed then the regular model. And the "_wing"s are the wings you see flying when a ship is destroyed. About the "laser" models, please, do NOT make them to big, that can really screw up the game. So after you replaced the models test the game and you will see how the models work. Keep on testing until you are happy with the result. Also, even although you might have deleted a .x file that you didn't need does NOT mean that the game thinks that it doesn't exist anymore, be careful and if it doesn't work, just change it back to the way it was before and try it again.
Now the backgrounds.
What kind of a background do you want? Stars? Nebula? Asteroid field? Remember, the internet is the greatest source of files you cant make yourself. If you can make the nebula's and the stars yourself then you have no problem at all. For you who cant, just go to Google images and type stars, then you will get enough to choose from. BUT be careful, the artists who made those images might not like it that you use then for this purpose, so ask for permission first or use a real picture taken by NASA or some space telescope, those pictures are usually not that important to the people who took them.
Ok, have the pictures? then go to the "images" folder and replace the files you see there with the ones you have made/downloaded, remember it is not enough to put them in the folder, you must also rename them so their names match those of the original files.
Now for the menu backgrounds, this is a little different. Go to the folder "data" in your game folder and ADD a little file extension to each file, the file extension is ".bmp", a common bitmap file. If you have done that then you can open and edit the files in the normal way. Just take away the ".bmp" file extension when you are done.
About the "dat..." files: One is the background for the menu and the other is a layer on the first background, so make sure that all the details end up on the second picture and that the first picture stays a starry background or whatever you want it to be, as long as it stays simple.
The last picture is a black picture, add some funny colors to it and start the game, I'm sure you will like the result. The planet texture "endor1" can be found in the models folder.
Now you want to change the radio messages from your allies, this is what you could call the story of the game, make up an interesting story and prepare your self because the next thing takes place inside the source code of the game itself. Tools: you need a HEX editor and (again) a lot of patience.
Open the .exe file inside the game folder with the HEX editor and search until you find some understandable text, somewhere in that area you will find the dialog, only here is the thing: every single letter and phrase has dot or a square between them, DO NOT CHANGE OR DELETE ANY SIGNS OR SYMBOLS THAT DO NOT APPEAR IN THE GAMES DIALOG AND LEAVE THE DOTS OR SQUARES ALONE, which means that you cant write more that there is already written and you must always keep a backup of the .exe file when you work with it, I will not be responsible for any damage caused to your game or your computer. Things will go wrong when you work with this but keep trying and you will get there. I do not believe that there will be any damage to your computer, however, in win XP it always says that the program has generated an error when you close the game, this is nothing and I honestly don't know why windows says that.
Now we need to change the music, this is easy, you go to the game folder and open a folder called "music". There you see the background music files, and to make it even easier, the files are ".mp3" files. This means that you can simply change it to any soundtrack or song that you might have. Do not forget to rename your files so they are exactly like to original.
If you want to change the explosions, look in the folder "shaders", in your game folder. Just edit the images in the folder until you like the result.
Now the sound effects, you do not necessarily have to change all of these files but if you want to edit them I would suggest using Audacity, a free sound and wave editor which you can use for music, sound effects and more. The sound effect files are in the folder "sounds".
Ok, just some advice for you who will release the game for download, set the scores to 0. When you play or even test the game the will be recorded. Just open the "score.dat" file with a text or hex editor and change it all back to 00.
If you have done all of these things, then even I am impressed, working with this stuff is only fun when you really want to do it. But if you have made it this far, upload your mod and let all of us try it. I will definitely try it! Just send an email to email@example.com or find another way to contact me, I promise that I will try your game!