A question this weekend: "What if I forget my Windows XP password?"
If your Windows XP computer is a member of a domain, please see this Microsoft KB articles http://support.microsoft.com/kb/321305 how to log on to Windows XP if you forget your password or your password expires, and http://support.microsoft.com/kb/306214 on how to create and use a password reset disk for a computer in a domain in Windows XP.
Otherwise, you might want to check a helpful article at... http://pubs.logicalexpressions.com/Pub0009/LPMArticle.asp?ID=305. I don't offer any endorsement for the third party method and offer it as a possible solution.
Also, Microsoft provides varying levels of support at http://support.microsoft.com/oas/default.aspx?gprid=1173.
One of my solutions to make sure that this doesn't happen: as I medntioned previously, first create a strong password for the administrator account your PC. When I installed the OS on my machines at home, I write the password in the OEM license booklet, along with the name, make and model of the PC to keep the information straight. It's all stored in a safe, secure place, away from prying eyes. ;)
Hope this helps and good luck.