Can't find that USB cable? Then look to see if your phone supports memory expansion cards such as MicroSD. Most phones are pretty light on built-in memory anyhow, so if your phone has a memory expansion slot, it can be a great way to give your phone extra memory and load your music files all in one shot.
To load music onto the card, you'll want to get your hands on a USB card reader. These things shouldn't cost more than $20, and they'll let you load music onto the card from both Mac and PC. Once the files are on the card, put the card in your phone, boot up the phone's music player, and if the files don't show up right away, look for a menu option where you can load music from the card.