If you don't want any of his music and just want your music back, then just connect your iPod and iTunes will transfer all your music across (you'll get asked a question Yes/No... choose Yes here in this case).
If you do want to keep some of his music to put with yours, download yamipod (free), which lets you transfer some songs from your iPod onto your computer. You can then put it into your iTunes library, then connect your iPod with iTunes running and choose Yes to the question... your songs and the selected ones of his you transferred with get copied.
http://www.yamipod.com