Well, I spent about an hour trying to get something helpful from the HP site. Not much luck.
Your mobo is the 246858-001, also called Spider.
All the Compaq info/specs on the site are really vague. i couldn't find a layout diagram at all.
Your best bet would be to email HP, explain what is going on, tell them which mobo you have, and ask them to send you either step-by-step directions or a layout diagram.