DVD Player Window Aspect Ratio - How to Unlock It?

Click "Video Zoom' in the "Windows" men. Check the "On" box at the top-left and uncheck "Lock Aspect Ratio" at bottom-left.

DVD Player, though, should set its widow to match the DVD. Your widescreen TV might be doing a stretch even if the DVD was set to 4x3. Are you sure Widescreen was set when you made the DVD? If not, you could fix it with myDVDEdit and burn a copy.
<http://www.mydvdedit.com>

That helps, but only partly. After you unlock the aspect ratio, you can widen the video, and it doesn't look "squished" anymore. But the window that the video is in remains in a 4 X 3 ratio, which means the left and right edges of the video is cut off. The window can be resized, but it remains 4 X 3. Is there a way to change the window's aspect ratio?

You can play the DVD with VLC
<http://www.videolan.org>
It has "Aspect-ratio" settings in its "Video" menu that will not clip the image.

The proper fix is to use myDVDEdit
<http://www.mydvdedit.com/>
to make a DVD with the correct aspect ratio setting.
Copy the VIDEO_TS folder from the DVD to your hard drive.
Fix the aspect ratio with myDVDEdit. See:
<http://www.mydvdedit.com/viewtutorial.php?t=27e&pg=forum>
(Ignore the part about a disk image, and the part about Toast.)
Use DVD Imager to make a disk image file from the fixed VIDEO_TS folder.
<http://lonestar.utsa.edu/llee/applescript/dvdimager.html>
Burn the disk image file with Disk Utility.

That worked perfectly. Thanks!