The spec for your motherboard can be found by Googling Motherboard Specifications, MS-7184 (AmethystM) and shows that it is a micro ATX that uses DDR memory and a socket 939 processor. As standard it does not come with a separate graphics card although it has a 16x PCIe slot. I tried to give the link but the PCA spam filter kicked in and won't let me post it but you will find it on the HP website.
The board will support AMD Athlon 64 X2 (up to 4800+) and Sempron (up to 3200+) processors so you could upgrade your processor speed and you could upgrade your graphics by using a separate PCIe card.
That said (and considering you have DDR memory not DDR2 or 3) you will probably find it cheaper to get a motherboard bundled with a more modern processor, better onboard graphics and DDR3 memory). Take a look at motherboard bundles from Novatech but make sure before you buy that the motherboard is micro ATX and will fit your case.
What OS version are you using because that will make a difference if you retain your existing hard drive and want to swap everything over?