Well, I'll preface this by saying I work for a company that sells stuff to do things like this on a grand scale. If you want to contact me privately regarding that after you see this suggestion, you may =] However, since your need seems to be small and since free is cheap, have you seen Big Brother? It does what you're asking and a whole bunch more and it's free. It's not fully functional as a full application or enterprise monitor, but it will solve your problem for sure.

good luck.

We speak the way we breathe. --Fugazi