Here is a couple of guides on how to do a new (fresh) XP setup
"Guide to upgrading (or new install) Win XP at Aumha.org by Gary Woodruff "http://aumha.org/win5/a/xpupgrad.htm
Step-by-Step: Clean installing Windows XP (Interactive Setup)http://www.winsupersite.com/showcase/windowsxp_sg_clean.asp
These assume you have the Windows XP CD and not a manufacturer's or OEM Restore CD (for the latter see it's documentation)
have your pc disconnected from the internet during setup.
When setup is complete, install your Antivirus program.
Then and only then, connect pc to internet, and then be certain to visit Windows Updates. Get current with MS updates !