How do I reinstall Windows XP - Please help

I have a Dell Dimension 2400, purchased/shipped on 1/1/04, with Windows XP.  I have all of the CDs that came with the computer, including the "Reinstallation CD, Windows XP Home Edition, Including Service Pack 1a".  I desperately need to reinstall Windows XP so that the computer is in the same state/condition as it was when I bought it. I have already saved all of my data onto CDs.  All of the instructions for this I have been able to locate on the web only apply to computers purchased/shipped after July 2004.  Can someone PLEASE give me simple instructions for how to do this or refer me to a website that has these instructions. Thank you very much in advance for you help.