I was working last week for a client and we came across a box whose admin password was not what we expected (or any of the many variations of what we expected), or any of the non expected variations. To no avail. However, one of our techs came up with this. This is a VPC floppy image (you can use VPC to create a real floppy disk). It contains a small linux build plus a password changing tool - which worked on XP SP2 just fine.
This floppy disk was developed by a Norwegian, and you can find more information on his web site