Open the case and check what motherboard you have, then post that here. We need the MAKE and MODEL number. With hp, dell and sony etc, they dont advertise what motherboard is included with the box/pc. They may give some details, like speed of cpu and its make, but not all the necessary details. If you can find the cpu socket from hp site, that would help but does not essentially mean that any cpu for that socket will work.
It's possible; same socket size, but may not work due to voltage differences among the various 775 cpus. Hp, dell, etc aren't designed for upgrading the cpu. The newer hp models list their tested model cpus on the spec sheet, but not yours. You have a 915g express chipset using 184 pin ddr pc3200.
i have this same computer with hp dc7100 4gb ddr, and the motherboard is 365865-001 LGA SOCKET 775 MOTHERBOARD. Can i upgrade the CPU to a dual core? Right now it has a p4 3.2ghz. I have ATI 6450 video card. 500w coolermaster power supply.