Hi Harry, I think I understand what you mean, I have recently changed from a 21 inch CRT to a 21 inch widescreen monitor, but have not encountered this problem. However it seems a common problem with people doing video.
The following links may help:
Link 1:
http://livedocs.adobe.com/en_US/Afte...6dea-7f3a.html
Link 2:
http://www.jeremymoore.com/AdobePremiere/PAR_Displays/
Link 3:
http://eugenia.gnomefiles.org/2007/1...aspect-ratios/
I think you may find the answer somewhere in these links.
Good Luck
Andy