To lock a Windows XP workstation you can use of the 2 methods below:
1) Keyboad Combination: You can lock your Windows XP workstation by Pressing the Windows key + the letter L to lock.
2) DOS Command: You can also lock a Windows XP workstation by typing the following DOS command,
rundll32.exe user32.dll, LockWorkStation
This command can be execute by either click on Start -> Run and typing the in the command, or by creating a shortcut.
3) Normal way: Click on Ctrl + Alt + Del, and select “Lock”