By a clean install I take it you mean reinstalling windows? No?
Anyway Backup your data that you want to keep(Burn to a DVD or copy to an external Hard Drive ect).Gather all your CD's with drivers on them. CD's that came with your PC if you cant find them or have lost them download them off the net and put them on a CD. Just remember that you will lose all data that you haven't backed up.
Pop your XP CD in, restart your PC and follow the prompts to install XP and format/partition your hard drive. Keep following all those prompts and from then on its pretty self explanatory.
Boot up into your newly installed version of XP download updates, install antivrus program and drivers and all your software that you use and volia (I'm pretty sure I'm failing french, did I spell that right. Volia ? Plus firefox doesn't correct french words.Heh Heh) You have a fresh install of XP. You should do this once every couple of years to keep your PC top notch.
I cant emphasize enough to Backup your Data and have your driver CDs
And remember that theirs no point in putting them on another PC on your network if you haven't got your network drivers installed!