This is the official Descent 3 SDK. Intended for use when making custom modifications for the game.
Where to Get Started
The first thing you need to do is go download the SDK. Next it would be good to choose a compiler. Currently there are only 2 that work for sure with the D3sdk. You can use Microsoft Visual C 6 under Windows. Microsoft Visual C 5 or 4 will work but there are a few minor issues with them. See the readme file for details. Then gcc for linux will work for Mods under Linux.
Here's the breakdown. Windows mods are done with VC. Linux mods are done with gcc (for Linux). For Windows OSIRIS you can use VC or gcc for Win32. Lastly you can use gcc for Linux to do OSIRIS.
If you don't know C++ but you're wanting to do mods, here are a few links to follow. It would be a good idea to know how to do this stuff before you dive in head first.
Devcentral.iftech.com
Netti.fi