umm, what is this server going to run anyway?
a quad socket 940 mainboard is expensive itself, but you also need 4 X Opterons with 4 way direct connect (800 series, 2 or 1 way won't work on quad boards)
on top of that, you need ECC RAM for socket 940 systems, which is more expensive
and you also need a powerful PSU. there are 4 CPU's in there.
anyway, Windows 2003 will recognise multiple CPU's, and also there should be several Linux OS's that do.