Yes it is!
It's not so stupid... it wouldn't have been the first time anything so elementary was the cause of something. Anyway, when I listen to music from Windows Media Player, everything works great, so I think there is really something wrong with Winamp itself... I think I'll try to reinstall it. Thanks for your help.
UPDATE: I found another thing. I've installed that Status2FTP Script which is working and not working. Could it be the cause? Ok, I'll try many things... Thanks for your help.