Tool to Monitor Internet Traffic

Hi All,

I am looking for a tool to monitor the internet activity in our network. We have ISA 2004 installed on Windows Server 2003 Standard.

Since the usage of internet is extremely high these days, we are looking for a tool that would help us in monitoring the usage of internet by our domain users.

We tried GFI Web Monitor but it took a lot of system resources and licensing was expensive.

Kindly post your suggestion.

Thanks,
Aravind.