You can do it but it's a lot of work. If it's a hobby type thing, I say go for it.
You'll need to pick up a new power supply as well, though, as even if you get a 20-pin ATX mobo, the wire configuration is different (I modded an ATX to work with a sawtooth, not a big deal but involved killing a line and splicing another).
Post pics if you decide to go through with it!