I have a couple of 200mhz Geode based PCs: B2B2C Wizards made by Fox. They're designed for POS (point of service, cash register like work).
They kinda suck. They don't have a L2 cache, and just 64mb of ram. Running windows is asking a lot (ran Windows ME for a while on it). Running linux is fine, but the bios boot up time is horrible and the lack of L2 really kills it...
Oh yeah, and the motherboard for it doesn't have PCI slots (a pci card would probably be bigger than this motherboard), it just has a PC104 (isa) connector, and the onboard sound is quite horrible..
Anyhow my post is rather negative, but if you want to give it a shot anyway, good luck
If it were me, and i had to go buy a small form factor motherboard, i'd try to buy one of the Pentium M SFF boards and give that a shot.