Username or EmailPassword
If you want something that's already available, there's no need to build it yourself. The one PC I built from scratch needed 2GB of RAM (expandable to at least 3GB) and I couldn't find a manufacturer that would offer systems with mobos that would support this. So I built it myself.
As for dual CPUs and RAID, you have to ask yourself "what am I going to do with this system?" If your answer is email/web surfing/IM, and stuff like that....just get a single PIII or equiv. That's still a pretty impressive email machine.