As you can see in this screenshot, the preview window is locked in the bottom part of the Vegas work area. It used to be free floating, but somehow I accidentally dragged it down there and it got stuck.

Thanks,

See those six little dots on the upper-left corner of the preview window? Click on those and drag the window out of docked mode.

Thanks for the help! I wish I could've found the instruction somehow by searching the Help file. I clicked on Help, Contents and Index, then typed in "Preview Window". There are a few tips about the Preview Window, none of which tells the user how to move it out of dock. Is there a manual somewhere that explains what each and every icon does?

Open the help file and search for "dock". That will show you how to undock the window.