This is a minor annoyance to Vista users -- less vexing than the now-blackened and disabled QuickTime controller bar which makes QT Movie NoteTaker useless.
Go to the Start Menu
Type "command" in the Search box
Then right click on "Command Prompt" shown on top
Select "Run as Administrator"
In the Command window, type (or right-click and paste):
You could also use an automatic technique from Winhelponline in File association fixes for Windows Vista.