Place the XP Cd in the Cd drive
set computer to boot from CD
start system....XP setup will start pick NEW installation and format the
drive when the option shows.
peter

Just boot from the Windows XP CD (change the BIOS boot order if necessary to
accomplish this) and follow the prompts for a clean installation (delete the
existing partition by pressing "D" when prompted, then create a new one).

You can find detailed instructions here:
http://michaelstevenstech.com/cleanxpinstall.html

or here http://xphelpandsupport.mvps.org/how_do_i_install_windows_xp.htm

or here http://windowsxp.mvps.org/XPClean.htm

or here http://www.webtree.ca/windowsxp/clean_install.htm

However why do you want to reformat and reinstall? In my view, it's usually
a mistake. With a modicum of care, it should never be necessary to reinstall
Windows (XP or any other version). I've run Windows 3.0, 3.1, WFWG 3.11,
Windows 95, Windows 98, Windows 2000, and Windows XP, each for the period of
time before the next version came out, and each on two machines here. I
never reinstalled any of them, and I have never had anything more than an
occasional minor problem.

It's my belief that this mistaken notion stems from the technical support
people at many of the larger OEMs. Their solution to almost any problem they
don't quickly know the answer to is "reformat and reinstall." That's the
perfect solution for them. It gets you off the phone quickly, it almost
always works, and it doesn't require them to do any real troubleshooting (a
skill that most of them obviously don't possess in any great degree).

But it leaves you with all the work and all the problems. You have to
restore all your data backups, you have to reinstall all your programs, you
have to reinstall all the Windows and application updates,you have to locate
and install all the needed drivers for your system, you have to recustomize
Windows and all your apps to work the way you're comfortable with.

Besides all those things being time-consuming and troublesome, you may have
trouble with some of them: can you find all your application CDs? Can you
find all the needed installation codes? Do you have data backups to restore?
Do you even remember all the customizations and tweaks you may have
installed to make everything work the way you like? Occasionally there are
problems that are so difficult to solve that Windows should be reinstalled
cleanly. But they are few and far between; reinstallation should not be a
substitute for troubleshooting; it should be a last resort, to be done only
after all other attempts at troubleshooting by a qualified person have
failed.

If you have problems, post them here; it's likely that someone can help you
and a reinstallation won't be required.