A good friend of mine made asked this question today. Normally I would just run mount -o loop -t iso9660 cdimage.iso /mnt/tmp but this lost soul lives in a windows-only world, so I set out to find the answer. I remembered something about Daemon tools, but an alternative came via Google from http://kennethhunt.com/archives/001125.html And as it happens, WinXPVirtualCDControlPanel is a free download from Microsoft.
Update 20050529: Local mirror.
Update 20050706: Yes, that’s a Knoppix ISO in the screenshot.