Read about this on Adam Kinney's blog. This is a great proof of concept for light gaming on the Silverlight platform. Looks damn good. Wish there were some higher res versions of the video.
http://www.innoveware.com/quakelight.html (scroll past the fold for videos)
There are some versions of Quake running in Flash, but they aren't ports they're just an interface over the top of the Quake code. The Innoveware Quake is a port from C++ to C#. It's still in progress, no real demo yet.