This mod from yamadawg37 changes the main menu music.
README and INSTALL INSTRUCTIONS
yamadawg37 | 13 Jan 09
Hey this is a simple mod that changes the main menu music to the very powerful "Requiem for a Dream" by Clint Mansell and his orchestra.
Simply extract the zipped file and put the gamedata folder into your main S.T.A.L.K.E.R. folder (usually C: -> Program Files -> Deep Silver -> S.T.A.L.K.E.R. - Clear Sky). If you've never played any STALKER mods you'll have to adjust the one line below in fsgame.ltx (change false to true; use Notepad) to look like this:
$game_data$ = true| true| $fs_root$| gamedata
----- Compatible with all patches
----- Credits.... Hey its just a song do what you want.