Instructions
Turn on your Xbox 360 and a controller. Plug the flash drive into a free USB port on the console.
Go to the "My Xbox" menu and select "System Settings." Choose "Memory."
Select your flash drive and choose "Music" or "Audio" as the item type. Select the MP3 file(s) that you want to transfer to your Xbox 360. Once selected, choose the "Copy" option and select your Xbox 360 hard drive (or memory unit if your Xbox doesn't have a hard drive) as the destination.