Help Problem Transferring files

[Bassoon]

Hi, my Tmobile G2 is not letting me transfer music files to my phone. I have previously done it and when I try and save the music in the same folder that my phone uses for music (that already works with my other music) it "saves". But when I disconnect my phone, the files aren't there and when I reconnect they aren't where I saved the copies previously. All the files are compatible with the phone (mp3s). Please help, this is driving me crazy!

Thanks