First off, that's the only non-nVIDIA card I'd own...and even then, just because of the power it packs. The Catalyst drivers still bite, and the fact remains that the nearly-equal GeForce 6800GT is about half the price with far better driver support all around.
I cringe to think of how muchCrapUSA is going to overcharge you on this build.
FYI, you simply do NOT need more than one gigabyte of RAM in your PC unless you plan to do a lot of video editing ect.
The addition of two more RAM sticks, or going from 2x512MB to 2x1024MB often causes substantial slowdowns in games.
The recommended amount of RAM in those games typically refers to the paging file, or Virtual Memory allotted. Less than that will cause stuttering or even crashes at times, but more physical memory, over 1GB, will not help that situation in most cases.
Hope it was less than $1500! Good luck.