24 pin ATX Power Supply with Compaq Motherboard

I have recently obtained a compaq deskpro 1.4 GHz (which I believe is
an EXS) and I am trying to add a new video card which requires a more
powerful power supply than the stock one. I purchased a new 500W PS,
but quickly realized that compaq sucks and they use a proprietary power
supply. I have tried to find the correct pin outs for the power supply
so that I can mod the ATX ps that I bought, but I am starting to think
that it's impossible. I have tried to find the compaq manual, I have
searched google, and I have also pulled out my DVM to try and figure it
out... no luck. I have seen a few posts on this group and I am hoping
that someone has figured this out. Is this possible, or do I have to
buy a new mobo??

Thanks in advance.