It won't. MP3's have been specifically designed to format a foreign hard drive upon impact as an anti-theft system designed by the music industry. I wouldn't try it if I were you.
And yes, I'm kidding.
As long as his computer can handle an MP3 (IE it's not a computer from 1986) it should be able to work just fine, as does most other media (I think). My friend Amber just moved to the UK from here and we still trade MP3's back and forth constantly so I'm pretty sure they're universal. The software to listen to the MP3 might be different, but the file itself should be readable no matter what country you're in. Just be warned that your music will sound much spicier their than it does here, and with waaay too much garlic, too.
"In an interstellar burst, I'm back to save the universe"