If you just want to sync your G2 once, that is to say copy all your music onto it, all you need to do is select all the songs in your library and drag them to any folder on your sd card.
If you want to repeatedly and automatically sync, like with an ipod, you need a program for that. Doubletwist comes with the phone and should work, at least mostly (podcasts are iffy). If you want a better solution, there are better apps on the market that will integrate with itunes.