Log web-traffic

Question

Hi Friends,
I want to program a service, that I can place on some computers (and no.. It is not for illegal purposes). I want the following to happen:

1) When the service is started, the user is informed that he/she is been logged.
2) The service registers everything the user does using the browser (only HTTP-traffic).
3) Before closing down the informations should be send to a shared server.

My problem is point 2? How can I track the user behavior (visited sites), and what can I track?

It would be ok just with Username, visited page, visittime. If it is possible to get information on how long time the user is on a page, then that would be great.

Best regards
Søren Jensen