I googled your PC and it uses a Socket 939, so you'll need to find a dual core CPU compatible with that. From what I'm seeing, the socket is pretty much dead technology, and dual cores were pretty much getting more involved towards the end of the socket 939's life.
Unless you're budgeted to just $40-50 for a used CPU, you're better off upgrading to the newer AMD CPUs like the APU, Athlons, etc. and maybe find some good combos. I recently got a budget dual core APU A4-3300 and a mobo for $59, so it shows how cheap some deals can get for decent parts
i want to upgrade to a dual core cpu but i dont know if the MB will handal it?
HP/Compaq like pretty much all big box OEM computers are going to be very limited in what can be upgraded and what you can upgrade to. Add to that the fact that it is pretty old and it is going to be even more limited and really whatever you upgrade to will only be a minor improvement. Really I would just get a new computer.