[Xavier]

What mobo is that rig on? If it's any good at all you could just buy a decent 2GB kit of performance RAM (will cost $50-$100) and overclock that Pentium D. It's been a while since I've seen somewhat report what they can achieve with those chips, but I seem to recall you can get up to 3.6-3.8 GHz out of them without too much trouble. Alternatively you could just spend $50-$100 on a budget dual core chip--the e2180 still has one of the best price/performance ratios on the market, and costs $70.

But all this depends on having a motherboard worth keeping...otherwise I'd probably recommend a Gigabyte DS3L for ~$90.

And of course if you're going to OC you'll want to upgrade from the stock cooler if you haven't already... the Arctic Cooling Freezer 7 Pro is a good cooler for $25-$30, or the Tuniq Tower if you want to go up to the $50-$60 range.