......we need more specs than that...woulda helped if you'd google your own PC and find out all the specs and post em. You shouldn't have bought a pre-built PC from HP or DELL or PeoplePC if you want to upgrade it...usually you gotta contact them for that just so they can throw in their own parts...the BIOS that comes with those computers...have absolutely no options because it isn't meant for users to get into that. I suggest you get the 'Hardware Guide for Dummies' book or something to that effect and start reading up on computers...technically yeah you'd need a new motherboard only to access more options and have more to do with it....but since you don't know how to build a computer......what do you plan on doing?
You need to do some research before you just say 'I got this HP machine...I want to upgrade and how much does it cost' you asked like 20 questions in that one sentence. 512mb RAM is pretty good, but you could use a faster processor I suppose...cause you got a XP 2200+ I believe...