Windows XP Home Edition or Windows XP Professional in a workgroup
To log on to a computer as the administrator to reset a password, when that computer is in a workgroup of more than one member, follow these steps:
1. Log on as an administrator.
1. Restart the computer, and then press the F8 key during startup until the Windows Advanced Options menu appears.
2. On the Windows Advanced Options menu, use the arrow keys to select Safe Mode, and then press ENTER.
3. Select Microsoft Windows XP edition, and then press ENTER.
Note In this step, edition represents the correct Windows edition.
4. On the To begin, click your user name screen, click Administrator, and then type the administrator password. (by default leave this blank)
5. Press ENTER, and then click Yes.
2. Reset the password.
1. Click Start and then click Run.
2. Type control userpasswords2, and then click OK.
3. Click the name of the user account that you want to reset the password for.
4. Click Change the Password, and then type a new password.
Note If you do not want to use a password, click Remove password, and then continue to step "e."
5. Click Change Password.
6. Restart the computer, and then try to log on to Windows XP again.
Source(s):
http/support.microsoft.com/kb/321305