I would like to record the traffic (including the POST data) coming to a website in IIS on Windows 2003 and/or Windows 2008
So that I may be able to replay the traffic to create a realistic stress test.
You could do this either on your IIS Box, or better by configuring your switch to mirror the traffic to another port and run Wireshark to capture on an independent machine on that port.
Configure Wireshark to capture complete packets, and only packets destined for ports 80 and 443 on your IIS server. Have Wireshark write out the data in PCap format for later use in PReplay.
You can also set a time limit for the capture, so you could capture an hours worth of data for later replay.
Colasoft Capsa has a free packet capture program that includes a packet player that allows you to "playback" a capture. That should do the trick for you.