You can reset the password in Windows XP outside of windows using a range of tools out on the web.
I find the Offline NT Password & Registry Editor the easiest. I've used it several times (...in genuinely legal purposes that is
It's posted in the thread ECTech has already provided...
...but an image file for a floppy disk or CD, plus detailed step by step instructions for this specific tool can be found here:
...Download is available at the bottom of that page.