to keep your MB, you can get a Q6600 (cheap option) or a Q9550 (pricier) either will 5 box. I use a Q6600 on a P45 MB with 8 gigs.
So RAM, OS, and CPU. After that I start looking to a new system. i7-920 systems are the sweet spot now, great performance and not too costly. Lots of upgrades still for most of the parts.
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