HT4014: About the Mac OS X v10.6.3 UpdateLearn about About the Mac OS X v10.6.3 Update
Quicktime X does not have the Pro functionality. It was released with that intended as an add-on in a later release. This is in part due to them completely altering the structure of the application. It's now multithreaded and uses helper applications for various transcoding steps.
The solution is to download Quicktime 7 from Apple and use that for the Pro functions: http://support.apple.com/downloads/#quicktime
A bit more to think about:
Quicktime X is more capable than Quicktime 7 of smoothly playing high definition video files that use modern, CPU-intensive codecs.
You can install both player versions on Snow Leopard systems (but not just the Quicktime 7 player/editor because it requires components of Quicktime X to function).
Thus, you can have the best features of both by using Quicktime 7 for editing & Quicktime X for playback.