From original post I summed U were getting new rig's, hence my request for full spec.
It now seems you are upgrading your current ones - right ?
so what do your current mobo's support ?
You can get good priced Tyan dual Athlon MP boards with onboard SCSI @ decent prices
If your getting a new mobo, get a dual CPU board but with one fast CPU, and add a second CPU later. - D'oh forgot can't have dual P4 --- maybe a Dual Xeon board with 1 Xeon to start ? -- or a dual MP board ( much cheaper )
Im going out right now, but if I get chance later I'll post some links to suggested parts / pre-builds.