here is some info in the baord
Santa Fe 3.x TriGem SantaFe KL133: 8800(P3091A-ARS), 8802(P3039A-ARS), 8805(P5187A-ARS), 8880(P3096A-ARS),
8882(P2901A), XT933, XT936, XT983, US 7935, A812, A815, A820, A830
saw it here
http://www.elhvb.com/mboards/Intel/HP.html
Are you sure though it is proprietary? I have replaced power supplies on HP Pavillions and they werent anything special so I dont think that part would be an issue....what about the back panel?? If the back panel is regular ATX I think you are in luck.
Are you sure its the motherboard? The gay little power supplies in those HP's are way underpowered and they have a habit of dying.
They DO make replacements for those microatx sized power supplies that are in the 200watt range as opposed to the wheezy 140watt range.
JP