I downloaded Sailing Software's media sync to sync music to my new Eris... am happy to say it worked (minus the licensed junk before iTunes stopped being a pain)!
If you are looking to sync music to your Eris and have a macintosh, try here:
Sailing Software media sync application.
You should be running at least 10.4.11 to get this to work. I am running 10.5.8 and it works just fine. I don't know about Snow Leopard...