I should of read your post completely. I thought you just needed to monitor your own bandwidth.

ops:
Is there a network security group in your office?
You won't exactly be able to install an app on your computer to hunt down the bandwidth hogger.
You will need to talk to the network administrators and work with them.
If you are an admin, take a look at this program called Eracent. It's a monitoring software that monitors installed software and licenses as well as what websites are being visited.
edit: Just read the previous response...
Installing a mandatory proxy is the best(only?) way to limit and monitor your users internet usage.