I would recommend buying an x800 gto video card with pci express that would fit and work in your system fine with the 300 watt stock power supply.http://www.newegg.co...N82E16814102602
If you dont want to spend the money on a video card then there is no way to play it on a pc.
You might be better of putting that money on a xbox 360 like you said.
The xbox 360 is a good system overall but it doesnt really own. It is overrated and it had problems on the first release of the units. Power supply/ overheating problems I believe... Hopefully they will fix it soon after the new year.
The xbox 360 doesnt own all pc's. There is insane pc's with amd dual core x2's with two nvidia 7800 gtx 512 mb cards and 3-4 gb of ram that would beat the xbox 360. Neither owns the other.