You can always try Limewire :)! The easiest would probably be to find someone who has a slightly older Mac. iTunes 1 will be on their install CD.

Macast
 

I'm going to have to throw in a vote for Macast, too. I have Macast and iTunes on my G4, but I never use the latter. Macast is just so much easier to use, and it just sounds so much better. I've been using it forever-- it's definitely worth the price, and it makes me a very, very happy camper.

And no, I'm not on the payroll.