My suggestion is to look at something like this: http://www.abmx.com/1u-supermicro-amd-opteron-rackmount-server-p-210.html 1U rackmount opteron from Supermicro that can have two dual core opterons and 4 drives and up to 16 gigs of ram. Supermicro server motherboards have always treated me well and performed well too.
I've had good experience with similar machines from Tyan : http://www.tyan.com/products/html/gt24b2891.html
