So far, the only game I've been following that is having PC performance issues is Brink, and that is due to an unoptimized driver-set from ATi, or perhaps some bad graphics programming from Splash Damage.
Either way: The OP's computer build is obviously from a gaming-centric pre-built company, who knows they can charge an arm and a leg to those who are not capable of building a computer.
What I would recommend is to wait until a month out from release to build a computer if you feel your current system won't be able to run any of the games coming out later this year. However, I built my current system 2 years ago, and only needed to upgrade the graphics card from a Radeon 3850 to Crossfire Radeon 5850s and I have not had issues running any game ported from the consoles to the PC. I've been seriously debating selling off one of the 5850s because most of the time the second one doesn't even get much of a work-load unless I'm playing Crysis....
Anyways, I would imagine a new system with a grand total of about $750 US dollars (including OS, monitor, kb+m, etc..) would run the game just fine and last quite awhile, as I recently built a system for my younger brother on a budget of $450 and that system runs all games maxed at 1080p.