Thanks for your patience everyone. Perhaps you can see what I mean in the following screen shots
the first picture the left cell is apx 169 pixels wide, the second its apx 184 pixels wide. Actually neither of these values are what I specified in my td width, which was 200
The systems I'm having the problem on are windows 2000 pro boxes running IE6 with all the updates. These are the computers that really need to display the site, so its pretty crutial that it displays properly on them.