Just position the board over the case wher it will be installed and mark the holes on the case. Pull the board back out and put stand-offs in the places marked. Some computers have golden stand offs that a screw goes into, some have plastics that a pointed screw goes into along with a couple of the other kind, etc. Then, simply insert the screws where the stand-offs are and start hooking up everything.
G/L!
If you need anything wlse, post it!