Your link is bad. Looks like you copied/pasted a truncated link.
Compaq was notorious for not following industry standards for systems. That includes power supplies. You need to determine if your motherboard is truly ATX-compliant. If it is, then the M4 would work with that system.
According to that, the motherboard is microATX. That may only indicate size and mounting, though. But it's certainly a good sign for you.Motherboard Description MIS name: MS-6577 M-ATX Rev. 3.1 (Giovani), Rev. 4.0 (Giovani2)
Here ya go.
A quick Google returned this: http://h20000.www2.hp.com/bizsupport...iesId=96300#A0
That's the spec sheet for this motherboard.
It has an ATX power connector, according to that.
There's a slim possibility that the board uses an ATX power connector, but isn't setup to the ATX spec. To be 100% safe, you may want to check the voltage on each line and compare it to the ATX specification. Even if it's not ATX spec, it's very likely you could make an adapter for it to use an M4ATX with this board.