I was given a computer by the guy upstairs, and I tried to change his name to mine, semi successfully. What I did was use the Windows Registry Editor program, "regedit32.exe" to search for ALL references to his name in the registry, and change them to mine. I also looked for all references to the name he gave his computer, and changed them to my name for it. Similarly I searched for ALL references to his password and changed them to mine.
In spite of that it still boots with his name on the start screen, and I have to erase it and type in mine and my password every time I boot the thing. I also rechecked the registry, and found that some entries had changed back to his name. I changed them to mine again, but every time it boots they change back to his name. Only solution as far as I can see is to format the HDD and reinstall Windopes.