how about posting the HP model number?
that way we can figure out what generation AGP port you have. different AGP revisions have slightly different slots
if the CPU fan had really failed he would be noticing other problems. but im pretty sure my dell's cpu fan isn't connected to the mobo

, so HP could be the same.
though a geforce4 would be a huge upgrade over the IG, i don't think an HP case has enough fans to keep it (and the cpu) running cool.
.02 and good luck