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I was thinking about a Dell Dimension 9200 with an Intel core duo (quad core E6600) 2.4, 2 Gig RAM, 256MB Nvidia G-Force 8600 GTS (PCI-e), 2x250 Gig SATA RAID 0 HD's.

I would not recommend Dell- they are not particularly cheap and overclocking is usually not an option. However, they are reliable workhorses (my company uses Dell exclusively- no blue screens so far!)

I just finished my new system that I am quite happy with:
E6420 (2.13), 2GB, 320MB 8800GTS, 1x120GB disk

The 2.13GHz chip can easily be overclocked to 2.3GHz and there is not enough disk activity to justify a RAID setup. 8800 with 320MB is a nice compromise between the more expensive 640MB version and the cheaper 8600s.