Network Tracking

I am having fifty workstations which are connected to a windows server 2003 server and the internet is shared from the server .My question is , am i able to implement a tracking mechanism without using any proxy server and track all the web pages which ever visited by an individual workstation connected to a network?If possible how to achieve that kind of tracking mechanism?Some workstations do open their web pages in InPrivate browsing , can we access those browsing history?

Since you're asking this on stackoverflow, I'm going to give you a programming answer:

1) Set up winpcap on the server

2) Capture ethernet traffic

3) Reassemble TCP streams

4) Parse said streams for HTTP GETs

5) Store the URLs

I'm sure, however, that you'll find several applications that do this sort of thing. Ask on serverfault maybe?