Quicktime is Apple so I'd doubt there's any official support for C#. I don't think realmedia files are playable on many players, but I found this on wikipedia:
http://en.wikipedia.org/wiki/RockboxBoth of those can be streamed over the internet though, quicktime on it's own if you have the player, realmedia you might need a flash program for I don't know (there's also Real Alternative which is codecs for windows media player, so you might be able to play it with the WMP Control). So you could always hack it by using an internet browser control and making it the same size as the video.
But basically what you're trying to do is create your own media player that can play any type of video, which is not easy to do. The best one out there (in my opinion) is VLC media player, and I don't think it can play realmedia files. Speaking of VLC media player, it's open source though I don't know what it's written in. Your best bet may be using that source code, which should be fine if it's not a commercial application. Either way it's not going to be simple.