If the account you need reset is one OTHER than administrator, your in luck. As the computer boots, press F8 and select safe mode from the boot menu. Log in as administrator (hopefully the password is blank) and reset the user account's password.
If the account you need to reset the password on is administrator, you will have to have a boot disk to reset it. My favorite tool for this is the Winternals ERD Commander (http://www.winternals.com/products/r...02.asp?pid=erd
), which is a windows recovery boot disk. I assume the machine you need the password reset on is the XP machine.
ERD costs lots of $$$, but I'm sure you can find another boot disk out there somewhere.