After some tinkering under the hood, I've found an answer to the problem. So here's a step-by-step guide to solving this problem in case others find themselves in the same situation.
The problem seems to be that there are .component files that are in conflict with each other in the QuickTime folder.
When solving this problem, I learned that I would have to use my Administrator password frequently in order to move QuickTime components in and out of the folder. (This must be a Lion thing. I never had to use my password as much with previous versions of OS X.) Make sure you know your Admin password.
Here's what to do to solve the problem mentioned above:
1) Go to Library>QuickTime. Inside the QuickTime folder, remove every .component file that doesn't start with "Apple." Copy these .component files to a folder on your desktop. (You'll need them soon.)
2) Start by moving the file called DVCPROHDCodec.component back into the QuickTime folder. You'll see immediately that this file enables you to see your DVCPRO HD file in both Preview and in QuickTime. (If that doesn't work, then I can't help you. This is the core file that you need to view DVC PRO HD files in QuickTime. Period.) Check your work by trying to view a test DVC PRO HD file.
3) Move the other DVCPROHD .component files back into the QuickTime folder. Test with your DVC PRO HD file again. Everything should work well.
4) If you have Final Cut Pro or Final Cut Studio, move these files back into the QuickTime folder:
>FCP Uncompressed 422.component
>LiveType.component
>Motion.component
Check your work again with your test movie file.
5) Now move the file DeskTopVideoOut.component back into the QuickTime folder. (I assume that this file helps to send video out of the Mac into an external device like a monitor.) Check your work again.
6) Move QTMpeg4Codec.component back into the QuickTime folder. Check to make sure everything is working.
Rinse and repeat with your other .component files one by one. If you find a conflict with one of them, then you probably can't use that component file in combination with DVCPROHD component files. Or you can see if the manufacturer has an updated .component file.
In my case, I had a component called "3ivxVideoCodec" that caused all of my conflicts. 3ivx is an MPEG-4 transcoder. Once I removed it, my DVC PRO HD footage worked like a charm.
I hope all of this information helped! -----Todd Ruel