I was playing it for a few days on my buddys free trial pass. Your rig may have more trouble with this than you think. This game is rough on your hardware. I think the comparison you made to oblivion is a good one.
My pc's a notch or 2 below yours, (p4 3.2ghz, x800xt, 2 gigs ddr400) and I could barely play it at "balanced" settings. Lol I actually blew my power supply playing it(it was a cheap POS I had thrown in there when low on cash.) My buddy's pc is brand new. He's using a stock e6700, 7950 gtx and 2 gigs of ddr2667, and hes able to play close to max. he just turns down a few of the lighting effects to make things smoother.
I don't think you'll be able to play on Max settings, but you should be able to play at "high" without much trouble. The servers are still very choppy though, so even if your pc can push the fps you can still expect alot of stutters here and there.
I would also recommend another gig of ram if it's in your budget. The game has no zones. The entire world is open-ended and you can walk from 1 end of the world to the other (which would takes hours btw) without ever having to load a zone. Because of that the game will soak up as much ram as you can possibly throw at it. The more the better.
IMO my pc is pretty much the bare minimum someone would need to play and still enjoy the game. As I said I could play at balanced settings but just barely. My framerates weren't terrific but they were playable-barely. Not sure what your cousin has under the hood but if its as good or better than mine he should be ok.
You can lower the settings alot lower than "balanced" but IMO the game isn't worth playing at that point. Instead of beautiful fields of swaying grass you end up looking at rectangular fields of green. instead of a large tangled forest you get solid brown trees with no detail. Some people might be ok playing things that way, but it was too bland for my tastes.
Anyway best of luck. The game itself is pretty fun, even though I didnt get a chance to get very far. They are still working alot of the kinks out of it now, but i think it has alot of potential.