I have a spare G4 sawtooth case, i'd like to stick a PC mobo in it. My 2 primary concerns are the screwhole lineups, and the pinout on the power button header. Anyone provide info on those? It's a MicroATX board.

Thanks.

You can drill holes and put your own standoffs in. as for the power button use a meter to find out which two are the correct lines. this link is for the opposite but it also has the pinouts.
http://www.xlr8yourmac.com/systems/ATX_G4_...to_ATX_case.htm

I think (by far) the important things to look out for are:

1. Most motherboards will interfere (specifically, the placement of the RAM modules) with the optical drive cage when the case is closed - choose carefully! Having a short optical drive can definitely help
2. The back panel will have to be extensively modified to accomodate the ports (serial, usb, video, etc)
3. A PSU mounted in the standard position will most likely cut off a LOT of airflow to the CPU, if not physically interfere with the CPU heatsink/fan

Having said that, I've got an Asus P5LD2-VM sitting in a Quicksilver case, using a 1U PSU mounted far inside the case (in a decidedly 'non standard' position).

Do some googling, there's a few sites out there that detail the installation.