I did a format and reinstall recently using the original CD. As someone above has said, do it carefully, being sure to press all the correct buttons in the right order. Be sure to have to boot order in the BIOS start with the CD.
I thought I had done it correctly only to discover that I had, in fact, simply done a re-install over the top. Second attempt much more care and attention applied and I got the proper format and subsequent clean install afterwards.