The Bios flash could work, but at teh same time it might not. Big name manufactuers like Dell, Gateway and anyone else you can think of, tend to order modifications of current boards. (Prime example is my friends dell has a Intel D865 board that was made by intel. its supposed to have an AGP slot, but dell put them out without an AGP.)
Depending on what was moddified on the board, a BIOS flash might do some damage (IE the missing AGP slot in my friends case. the new bios had agp settings that kept erroring at post since he had no AGP SLot), so just be carefull.