Yeah, don't get anything under a 7800 GT for UT2K7 - That card will set you back at least $400 but that's the price you're going to pay if you want to play a game which is the most demanding engine around... (and still has some time to go before it's released!)
I would wait until ATi brings out all their cards though (end of OCtober) because is the new ATi card is the powerhouse some people have beentalking out, it will surely make those prices drop by 20% or so.