If you still have it, you could also try using the foam that comes in the box with the motherboard.  If you put that between the motherboard and the wood it will keep any solder points from have pressure on them, and will probably help keep the board from sliding around (which it might want to because of the torque from the power cable).

Also unless you don't plan on putting any cards directly into the slots, make sure you put the motherboard close enough to the edge of the wood that the end of the card sticks over and can get pushed down into the slot all the way.