FAT32 or NTFS? If FAT32, see below. If NTFS, get something like NTFSDOS Pro at
SysInternals and then see below.
Using a boot disk, boot up to DOS mode, go to the \WINNT\SYSTEM32\CONFIG folder, and delete/rename the file called "SAM." Reboot, and just hit enter/return at the Administrator login. Voila.
BTW, you will lose some user account information -- but that's the price you pay for forgetfulness. You're welcome.
