Actually its something I did a few years ago for the exact same reason as hurgh. In effect it is the same idea as Matthew's latest contribution to the thread.

I made a screen saver that didn't save the screen. Sounds funny huh? All that it consisted of was a small password window which could be moved around etc. The rest of the screen was perfectly visible but of course could not see any mouse or keyboard events at all.

In the company I was working at, the "no save screen saver" became very popular amongst staff who wished to go to appointments but leave their electronic diary set to display the days meetings etc. This way, a colleague coming to see the person could easily see when they would be back.

The screen saver accepted the user's password and also a system password known only to the system admin staff. This meant that when we went to a user's machine to fix a fault or whatever, we could get in even if they were not there. Nowadays, Windows NT offers the same thing although "back then" it didn't.

Yup, the no save screensaver was quite the technological breakthrough in it's time

Perhaps you can do the same thing to solve your problem. As long as the password was not know to your pesky colleagues, then you can easily safegaurd your system while the backup runs.

Regards
Paul Lewis