Between those two cards, the X1950XT is better. Look here.
The 8800GTS 320MB is currently 90 bucks more than either card. And that's the cheapest one from Leadtek.
I am using the X1950XT on Neverwinter Nights 2 and play it on a 22" 1680x1050 screen. I can play the game with most of the eye-candy turned on.
If you are on a budget, the best thing for you to get is the X1950XT and an extra gig of ram which is cheaper than 1 8800GTS. Only get the 8800GTS if you already have VISTA. If not, than the 8800GTS will be pointless as you won't be able to run DX10 games with DX10 turned on anyway.