compfused

I am configuring a dell vostro, and I have some options for the processor that I don't really know what to choose. I want to do SOME gaming, not like super high graphics stuff mostly like dungeon seige 2 kinda games so I wanna know what processor is going to be the best. I have the 1.6, 1.8, 2.0, and 2.2, I know the fastest is the best but I don't have alot of money and that puts me at 1298, where as the 1.8 is 1063. (The laptop has 2gb ram and a geforce 8600 so I'm only worried about the cpu) Will the 1.8 be sufficient? SHould I just suck it up and get the 2.0 or 2.2...Help!!!!

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Computer I have/Computer I want
2.0 ghz c2d/C2Q Q6600 2.4ghz
2 gb ram/2gb Ram
8600m Gt/8800gts
120gb HDD/250gb 7200rpm
Bluetooth/Gold tooth?
Vista Business/Vista Ultimate 64 bit