You probably have the socket 478 variety. You should be able to take up to a pentium 3.0 or 3.2 northwood "c" series cpu. I would not use prescott (1 meg cache) cpus as your custom dell heatsink may run too hot with it. I used a 2.8 "c" series northwood in my last Intel build, and it ran fine, with temps in the 40's to mid 50's. The northwoods have a 512 L2 cache. Use pricewatch for comparisons. Northwoods are getting scarce now. Starmicro is one place that had some selection, but I've never done business with them. Remember also that your motherboard is not set up for running in dual channel mode for the memory, so the cpu will not reach it's full potential.