Hey, I've got just the thing:
TimeSnapper.
it is a SUPER program that takes a screenshotevery x amount of seconds. What I did on my LAN network is I put TS on all of the computers, set the output folder as a hidden one on the HD, and then made the output a shard document. To make use of this shared document, run the Network Setup Wizzard in the control pannel. Turn on file/printer chareing for all computers. Then find out the IP of each computer. to do this, go onto each computer and bring up the runbox by going to start>run. then type cmd. then type ipconfig/all. The line htat says "ip address" is the number you write down. then when finished, (and when the output folder is a shared doc), go into internet ex and type in \\xxx.xxx.xxx.xxx "x's" being the ip address.
here is time snapper
http://www.timesnapper.com/index.html