Check out:
http://www.tyan.com/products/html/opteron.html
Their two most recent boards for that line are:
http://www.tyan.com/products/html/thunderk8hm.html
http://www.tyan.com/products/html/thunderk8hr.html
You might be able to get a board with very similar performance to the Tyan Thunder K8WE (S2895) but at a much lower cost now. (Not to be confused with the Tyan Tiger K8WE (S2877) board)
Still nForce Pro 2200 + 2050 was the first true dual PCIe x16 chipset
, out well before all the other nForce 4 ones
.... but that doesn't make that much difference, it is the other features that do. (eg: Aggregate memory performance between 2 processors).
A 2nd Opteron 200 series CPU (single core like what you have now) will not cost you very much at all.
No doubt all the chipsets and price ranges will sway you, just fire me a PM (Private Msg) or é-mail me, or MSN me. (My details are in my profile and in contact section of my
very dodgy website - see my signature).