It sounds like you want to start over with a fresh installation of Windows XP, wiping out everything that's there now. If that's the case you can click here for step-by-step instructions, along with select screenshots down the left-hand side. Just make sure you have backed up all of your files as this will leave nothing behind.
Hope this helps,
I was trying to format my c:. I keep getting an error not letting me format. I read somewhere to go ahead and install xp home over xp plus. problem I have now is I have two operating systems to choose from when starting. I would still like to format and start with a clean install.