Try Everest Home Edition and it might tell you what kind of Mobo you have, but knowing dell you won't find out.
AMD Athlon 64 3700+ San Diego @ 2.8GHz
DFI LanParty nf4 ultra-d
eVga 7800GT 256MB
1GB OCZ extreme series (2 x 512)
OCZ 550 Watt PSU
Samsung 200GB 7200rpm
Tsunami Dream Case