"he said it would work"
As you bought it on this basis - why not ask *him* how to make it work - the point being that if it can't be made to work then you can at least ask for your money back.
Have you tried with the AIMM in and out?
Have you looked in the BIOS for a setting which disables the AIMM?
Have you asked Compaq - there support is very good usually.