Need some advice on gaming rig

This is my first attempt to build a computer(with the help of my cousin) and I was interested in the Alienware Area-51 X58. But I'm trying to build a similar one for alot cheaper for budget reasons. I play Crysis, Call of Duty, and World of Warcraft. I was wondering if anyone has any idea how well my computer can handle these games or should I change something.

Intel Core i7-920 2.66 GHz 8MB
1.8GB NVIDIA GeForce GTX 260
6GB DDR3 SDRAM at 1333MHz

I was also wondering about a GTX 260 and how well it performs. I've heard it had some problems with running just WoW and not other games.....

I plan on running with Vista 64 bit or maybe switching to Windows 7....does anyone use Windows 7 for their gaming computer?

Thanks

the resolution i play on is 1400x900

A GTX260 is overkill for that resolution, and the extra video ram is a waste, i can run crysis smoothly on high with a 512MB 4850 at 1280x1024, a 4870 would likely max it out which still being way less than that GTX260, the cheapest one i could find on newegg was 200 which is the same price as a 4890 and only a bit less than a GTX275.

Here's a good deal on a 4870

http://www.newegg.com/Product/Prod [...] 6814121291

and for the future you could add another and crossfire them