Vegas Pro 8.0c on Vista 64 (also repeatable on VP8.1) QT on the system is 7.5.5
When I go to File > Render As...
Save as type: Quick Time 7 (*.mov)
Template: <choose any>
Click on "Custom..."
Go to Video tab in the custom template
Change Video Format to "MPEG-4 Video" and click on Configure...
Does anything happen when you do that? I expected some configuration options to show up, but nothing ever happens. It works for every other format that I click Configure for.