What is this rig going to be used for? If you plan on gaming - that onboard Radeon won't get you very far.
Some concerns -OS
I'm guessing you have an OEM copy of XP from HP? If so, it's probably going to try and load all the HP drivers right away which will prevent you from booting. If this is the case - you MAY be able to boot into safe mode and set everything to generic. If you have a real copy of XP, this won't be a problem Motherboard:
That is a micro ATX board. What case are you using? If it's the factory HP case, you'll want to check with them whether or not a mATX motherboard can even fit inside. You see, HP often uses proprietary parts so that standard items will not fit. (e.g You have to buy **** from them since only their parts fit)