HELP! Everything is set for 720x480, but the TV/DVD player is playing it with all four corners cropped. Please advise!

Does your external monitor have underscan capability? or, does your converter have underscan capability?

I don't know what underscan is. The mpg file plays correctly on the computer, and the preview plays correctly in Sony DVD Architect, but the burned DVD appears cropped on multiple TV/DVDs.

I also just have one large monitor on this system.

Dana, underscan/overscan (http://en.wikipedia.org/wiki/Underscan) has been an issue with video since it's inception.
It has gotten better over the years but is still an issue, even with LCDs, Plasma sets and video projectors.
In a nutshell, you should allow at least a 5% border for any critical video and 10% for titles to ensure that the necessary information will be seen on your TV screen.
The Preview window in Vegas has a Safe Area overlay (looks like the # symbol) and the settings for it are found in Options-Preferences-Video.
I always have it enabled any time I'm doing titles.
The defaults are 10% for Safe Action and 20% for Safe Title.
While these are over the SMPTE recommended standards of 5% & 10%, at least you'll be sure that you'll see what you intended.

Thank you.

In DVD Architect it won't let me zoom out; it will only let me zoom in.

That's correct Dana.
You'll have to go back into Vegas and use Track Motion to zoom out as desired.
At least you know what to look for know and can be more aware of it.

Thanks Mike,

I'm used to a degree of cropping, or underscan, but I've never seen it that bad. I'm surprised they don't have a zoom out feature to compensate. On this job my wmv and mpg will be different.

Dana, I've seen 20-yr. old TVs that I know I could get away with a 5% margin for titles and almost-new ones where a 20% safe area (for titles) wasn't enough :-)