I recently bought a Linksys BEFSR41 router and set it up on my G4. You should be able to access the router from your Cube if you can get that link going (I'm totally unfamilar with wireless stuff). My IP address I typed in was 192.168.1.1. I think this is standard for a lot of routers out there, but I could be wrong. My setup was pretty much plug and play.
If you can test that you have an internet connection via your DSL modem, and you can make sure your router works, it should work right away.
One thing you could try is directly hooking up your Cube to the DSL modem with the cross-over cable. If you get internet from there...
Hook up your router to your DSL modem (with standard Ethernet cable) and with another standard ethernet cable, hook your Cube up to the router. You should see some lights on the router indicating your Cube's network card is up, and you should get internet. If that works, then try wireless.