Here is a way (in Windows XP) that you can increase the security on your computer. Using Syskey you can require a special floppy to be inserted in order to log on to the computer. If you do not have the floppy, you or anyone else who tries to log on will be locked out. So here is what you have to do:

1. Click Start, click Run, type in Syskey and click OK.
2. From the Securing the Windows XP Account Database window that appears, click the update button.
3. The Startup Key window will appear. Ensure that System Generated Password is selected.
4. Click Store startup key on a floppy drive. Click OK.
5. Make sure there is a blank floppy in the floppy disk drive.

Once you create the floppy disk, you will be prompted for the disk before accessing the Windows logon screen. If you do not have access to the floppy you are out of luck, as they say, and will not be able to log on.