If you're using the Developer Tools, just double-click this file and change the value for the key from No to Yes. Save the file and quit PropertyList Editor.
If you're editing via the command line or your favorite text editor, you need to first convert the preferences file to XML format in Terminal:
$ cd ~/Library/Preferences
$ plutil -convert xml1 com.apple.quicktimeplayer.plist
Edit the file, changing the QTPMovieInfoShowPanel key to look like this:
<key>QTPMovieInfoShowPanel</key>
<true/>
After editing, you can convert the plist file back to binary format:
$ plutil -convert binary1 com.apple.quicktimeplayer.plist
Now launch QuickTime Player, and revel in the always-visible Info window.

