First published version, looking for comments & test. Read more for install instructions.
For non-modded clients: extract the file InsaneSeasonV1-1-2.rar on your desktop. Inside, you will find "gamedata" folder. Then, open the folder where you have installed ST.A.L.K.E.R. SHOC (the default route is C:\Program Files\THQ\S.T.A.L.K.E.R. - Shadow of Chernobyl) and find the file fsgame.ltx, open it and in the second line, will be something like this:
$game_data$ = false| true| $fs_root$| gamedata\
Then, you gotta change the first "false" to "true", and should left something like this:
$game_data$ = true| true| $fs_root$| gamedata\
If you want, copy and paste the last line, but would be better if you only change the "false" to "true".
Now, copy and paste the "gamedata" folder on the S.T.A.L.KE.R. SHOC folder. if you did well, the would be two folders only; "bin" and "gamedata". Now, you can start playing the Insane Season.
For modded clients: extract the file InsaneSeasonV1-1-2.rar on your desktop. Copy and paste the "gamedata" folder on S.T.A.L.K.E.R. SHOC folder. If you have other mods installed, there will ask you if you want to paste and replace it all. ATTENTION. if you replace it, your other mod could be affected. So, choice if you want play this.
Once you have everything installed, let's play.