Some days ago I had a pc in front of me with windows xp prof installed - but nobody could tell me the passwords. Setting the system up from scratch was not a solution, a way to enter the system had to be found. Looking for a tool that could break or reset the xp password I found a great tutorial at linuxquestions.org.
The solution was very simple: First I burned an up2date knoppix and started it on the computer. Then I had to install chntpw via the knoppix pakcage manager - it is contained in the unstable packages and an update of the package db was required before. Fortunately ntfs capability is included in Knoppix and I could simply mount the windows partition readwrite. After that I located the file “SAM” that contains the windows passwords and reset the password to an empty one with “chntpw SAM”.