I would think that since Compaq was sucked up by HP a quick (cough) call to the tech support can give you the information you are seeking.
Ask them specific questions such as...
What kind of memory does my motherboard support?
What CPU's and CPU speeds does my motherboard support?
Can I buy other memory or CPU's from 3rd party's or do I have to buy from HP/Compaq? (The reason for this is because in some instances, Compaq only used motherboards that supported their own memory)
In addition, I noticed the tech support site for Compaq is still up. You may want to begin your search there.
http://wwss1pro.compaq.com/support/home/index.asp
However, I think a call to them would be your best source for information. Just make sure you look for you serial number tag located somewhere on your PC. They will probably need it to look up the specs.[/i]