windows - monitor local network traffic issue

I am using Networking Tab of Windows Task manager to monitor local network traffic to test how much bandwidth my application will use. My scenario is, I will use a local console client application to send data (using Http POST method) to local IIS 7.0 server.

My issue is no traffic could be monitored using Networking Tab of Windows Task manager. My environment is, VSTS 2008 + C# + .Net 3.5 + Windows Vista x86 Enterprise. Any ideas what is wrong?

thanks in advance,
George