Here are a few good links on IIS 6 compression.
IIS6 compression by Scott Forsyth
http://weblogs.asp.net/owscott/archive/2004/01/12/57916.aspx
Enabling HTTP Compression
http://technet2.microsoft.com/WindowsServer/en/library/ae342c42-fbc4-4ab7-b9ac-20a89f0fa4ad1033.mspx?mfr=true
Customizing the File Types IIS Compresses
http://technet2.microsoft.com/WindowsServer/en/library/9fbab3d5-6f02-4c2c-a018-21e1f69d986e1033.mspx?mfr=true
Tx,
Steve
Pondering Thought 
This Microsoft Bug has really scared me off of compression on IIS for awhile. http://support.microsoft.com/kb/831464/
Putting a patch on the server is not so bad, its the part about having to ask clients to clear their cache that makes me quiver.
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