Ya'll have probably seen this by now, but heres a schematic of the MT drive and steering h-bridges:
As usual, don't go blindly trusting stuff you see on the 'net. I did my best, but at 3AM 'best' ain't that great. If you see a mistake, let me know so I can correct it. Also, if you reproduce this elsewhere, if you can, try to link to the original on my webhost so that any corrections will propagate.
You'll need to remove some of the driver transistors labeled 'D9D' where you swap in FETs. Basicly just set it up like the SE h-bridge and it will work fine with MOSFETs. If you don't mess with the D9D parts, the FETs might not work at all. They certainly won't work as well as they could.
On the plus side, the board uses a 5v supply, so there is plenty of voltage for any reasonable FET.