Are you sure you are not eavesdropping? hahahahah
Anyway, the best software to eavesdrop, opps... my bad. is from
www.remoteanything.com
With a footprint of only 90kb (for your slave, a.ka. for the stations) nothing will beat that. Not to mention, you can send the 'slave' configuration through email, let them click on it and bang! you can see the whole of their computer right in front of your eyes from their screen unto their precious harddrives.
Behind a firewall? well, thats no problem, because remoteanything uses http to send connection. And lastly, with their so called desktop management, you can peek hundreds of computers all of the same time.
I hope this helps your research.