Macworld forum visitor, JetPilot, was dismayed to discover that when he or she visited Eithne Ni Bhraonain's (aka, Enya) website and attempted to stream a video saved in QuickTime format, RealPlayer opened instead. After some poking around, I discovered the source of the problem.
The movies on Enya's site are in this format: rtsp://qt.WBR.com/enya/videos/qt/some_enya_movie.mov. So yes, even though these clips are intended for QuickTime, Real butts in and hijacks them. What appears to cause this usurping of QuickTime's property is that "rtsp" (Real Time Streaming Protocol) entry at the beginning of the links.
The problem is that RealPlayer needs to be told, in no uncertain terms, that rtsp streams are not its property. To make this clear, launch RealPlayer, select Preferences, choose Media Types in the resulting window, uncheck the Real-Time Streaming Protocol option, and click OK.
What's that? You say that the RTSP option is unchecked and RealPlayer continues to lust after this Gweedore-native's work? That's what I mean by "in no uncertain terms." Even if RTSP is unchecked, RealPlayer goes after these things. Therefore, you must enable RTSP in RealPlayer, click OK, then disable it, and check OK one last time. Doing so appears to give RealPlayer the hint as the videos then launch with QuickTime Player as Ms. Bhraonain intended.