Virtualbox does support 3D hardware but its still experimental. I have a 4Ghz Quad core with 8Gb of ram and my VM is Windows XP with 2Gb and dual core and I was able to play the Back to the Future games with it. I rarely use them for gaming. I think VM's still have a ways to go before real gaming will be possible. Back to the Future is a very low resource game and I had a few problems making it run right. However, once I had it working it ran great.
I don't see a VM playing Modern Warfare 3 any time soon. I think the problem is that in order to use hardware 3D acceleration the VM can only interface with hardware though API's and without specific support by hardware manufacturers its going to be hard to make it perfect. We can't even get Nvidia to help with good Linux drivers I don't see them wasting time with VM's any time soon. I think it all comes down to horse power. If you though enough pony's at it then anything will work.
I do almost all of my gaming on the Xbox. I have two of them, one on the shop and one in the living room, and the nice thing about those is that I know any game I buy will work perfectly and I don't have to mess with it. I honestly abandoned PC gaming years ago because I got sick of upgrading my video card every time a new game came out. Today the only reason I want a 9 series Nvidia card is for Cuda.