This cpu is commonly found in newer business class all in ones, and truthfully, its pretty efficient. The cpu is not specifically built fr gaming, however, WoW isn't a taxing game and with that card, it would not bottleneck. I'd recommend up to a gts 250 or radeon 4850. If you have Ddr2, I'd make sure it has the 800mhz vs the 667, so you will not have to upgrade that. That computer is not inherently a gamer, but should run Wow just fine for you. However, I might say as a reference from the DDR2 and the dual core at a high clockspeed, it may be suggested taht this machine may be tricked out about as far as you may go, suggesting it may not be that futureproof. but for those games, go ahead, look for a price of about 600 though.
With everything I'm getting in it its going to be $726 so I might be able to upgrade... and yes it is 800MHz... I was also wondering how do you think it could handle Modern Warfare 2? Or Counter Strike Source?
Go with the 5670 if you can, itll give you a nice boost at all resolutions for only 30$ or so more.
As for the 5570, its fine for more casual games like WoW and CSS, mw2 it should be fine with, with some lowered details