hi what format shoudl be the best to use to load musics in the mod ?

So far I used wav but converting the mp3 I am using to wav increases their file size by 40 times , the game seems not to read mp3 ... so whats the best to use them like?

You'll wanna look at converting them to xwm files.
Here's some dudes tutorial; https://www.youtube.com/watch?v=mIp9a5IUc44&feature=youtube_gdata_player

Definitely XWM. Getting the CK to accept them requires you to manually type in the filename with the xwm extension. You wont see XWM files in the list as a choice, but you can still type in the name and hit OK and the game loads and reads them just fine.

Thirded for XWM. For some reason WAV files cause crashes on some systems.