Good news - got the videos resized so they fit and the bars are gone. Here's what I did using all your suggestions (and lots of experimentation!):
- re-downloaded from stock site in WMV format
- opened in Movie Maker
- used Project tab to check ratio: all were wide screen
- saved each one as MP4 movie using "recommended settings"
- changed sizes to 250W x 180H (frame sizes) using online converter
- converted resized images to FLV
- uploaded to WordPress site using Add Media
...and they look good. To be honest, I think they are slightly stretched vertically, but not enough to be noticeable by users.
I still need to learn a lot about this whole video issue, but thank you all for working me through getting these three looking better on our site. That was the urgent priority!
With many thanks and much appreciation,