My plan was to upgrade in steps - RAM first, then mobo/processor. Unfortunately, I didn't do enough due diligence on the RAM selection given my old mobo, and it doesn't work. Which means I get to upgrade the mobo/processor a little sooner.

I've bought 4GB of RAM:
2x - 1GB 184-PIN Reg DIMM 128MX72 D DDR PC3200 400mhz, CL3, ECC, REG
1x - 2GB 184-PIN Reg DIMM 256MX72 D DDR PC3200 400mhz, CL3, ECC, REG

I'm putting together a software development workstation, not graphics intensive, but I do intend to buy two large (24" ) DVI LCD's sometime in the future if that matters. HD performance doesn't matter as I'll mostly be using NFS over the network. It's primarily processing/ram performance I want.

Any suggestions?

First off I need the system specs is it Socket 939?

Because once you upgrade you might not able to use those RAM because you might have to change over to DDR2, which means you will have to purchase a new set of RAM which is quite expensive.

I want to replace both the processor and mobo together actually, but I want to stick with the already purchased RAM.

Here check this out:

http://www.newegg.com/Product/Prod [...] 6813157107

Meh. Supports a max 2GB of memory.