Actually one of two ways might work.
1)Depending on which P4 you have and assuming you want to keep FSB at standard spec's
If FSB=100, you need a board that has BIOS allowing 1:2 DRAM ratio and for FSB=133, you need a BIOS with 1:1.5
Btw, if you find any board with these settings please make sure to let us know cuz I don't know of any myself.
2)Find a board that supports what's called
Async clocking mode between CPU and DRAM, that way you can lock CPU FSB and manually float your DRAM frequency.
FYI, I don't have an 845 based Gygabite board so I don't know if this feature works
Peace.