Go to Options >Media Card. Turn on Mass Storage Mode. Then when you plug the BB into the computer the BB should show up as a disk drive and you can copy/paste your mp3's into the music folder on the media card.
gmot...Did you format your card in the device? Go to Options >Media Card. Hit the menu key (left of trackball) and select "Format Card." This will erase anything you've already put on the card so make sure you back it up.
Once that's done. Enable Mass Storage Mode in that same menu screen.
When you plug the BB into your computer go to My Computer and see if you see a new removable drive called "BLACKBERRY F:" (or whatever drive letter your computer assigned to it.
when i first plugged the bb into my laptop it asked me if i wanted to switch to mass storage and i did and that as far as i have gotton if you guys havnt noticed im electronicly stupid soooo im sorry and thanks for trying to help me