Network monitoring on a basic network

Morning all im currently sitting with a predicament, we have 20 computers in the office and this is leading to people downloading but due to the nature of our business limiting the internet connection is all i can do but still they are downloading what can i use to minitor there activities in the line of free ware and what are the best ways to do it.:confused

 

Have a look through here for starters: http://majorgeeks.com/downloads39.html

 

edit: read your question wrong...

collins got it