Companies that I know make Dual AMD CPU mainboards are Chaintech, MSI and Asus. Most other manufacturers only deal in Intel dual CPU systems. I personally would suggest going with something like this:
http://www.tigerdirect.com/applicati...000&CatId=1231
or if you want to spend the money:
http://www.tigerdirect.com/applicati...X51&CatId=1182
I don't honestly see the benefit with dual CPU unless you are running a server and the above samples would more than accomplish what you are looking to do (and then some).
But I can be (and often am) wrong. But I thought I would share anyway.