how can i wipe out my hard drive to do a clean install of windows xp?

My registry is fine. I cleaned it!!!

My laptop will not boot up and it keeps saying strings not recognized.I got the computer free and if its gonna be expensive I would like to know how much but if I can hook it up to my desktop or download software that would be better because I have no car or any body reliable to ask for a ride.It’s an HP Pavilion zt1000.

any Registry cleaner?

do you know any program with which to clean the registry?
a freeware, easy to use