User switching is the fastest way to switch to a different user account.
This lets you have several accounts logged in at the same time, but only one of them interacts with the keyboard, mouse, etc. and is open, while the rest continue to run open programs.

To enable fast user switching:

1. Go to Control Panel and click on user accounts.

2. Click the User accounts icon in the Control Panel icons section to open the User accounts window.

3. Click “change the way users log on and off”

4. Check the box “Use Fast User Switching”

And you’re done! To Switch users, open log off from the start menu and click “switch user” or just press Windows Key + L.

More Cool Windows XP tips & tricks HERE