I've not been able to locate a password protected sreensaver which allows for many usernames and passwords, but you could do this quite simply in Visual Basic (if you or a friend has it).
There are many sample Visual Basic password protected screensaver programs on the web. All you would need to do is create or adapt a routine which would, upon interruption of the screensaver open a small window to ask for username and associated password, rather than just the password.
Google this: "visual basic password protected screensaver"
If you go to a Visual Basic forum, you could ask if any one has actually programmed something like that or if anyone could.
Failing that, you could assign a different screensaver to each user and a different password to each screensaver.
Look here for some free screensavers with password protection.
http://www.passtheshareware.com/ss_util.htm
One of the "slideshow" type screensavers would work well. Just use 1 or 2 images to keep it small.
You might have to have several copies of the screensaver, each one kicking in when that particular user was logged on i.e., "johnss.scr", "antss.scr" etc.
Hope this gives you some ideas
