The Well-Tuned Server, Part 2
Subject:   http compression works pretty well too
Date:   2006-01-06 15:15:02
From:   ServeThis!
I have noticed a 65% bandwidth reduction as well as increased throughput during high traffic with IIS 6 compression.

This article shows you how to enable it

Also a nice tool that can show you what your site can gain since IIS 6 doesn't have any reporting