i used to have a hp pentium 3 system. the psu had a 3 pin connector that went into the motherboard. i think it was for the psu fan. if you are getting a generic psu then you dont need that connector. also as you mentioned that hp is not making your part anymore then there is a chance that a generic powersupply may not fit into your compaq chassis. but that is only assuming that your system is relatively old and comes in a small chassis.
that could mean buying another chassis as well as a psu. depending on what your friend needs a pc to do, he/she could just buy a new dell for like $300 after rebates. if its for gaming then custom build a rig.
cdkiller [everything is to be replicate]