Okay, so I've got things pretty much the way I want them with this fairly heavily customized version of the Thesis template for WordPress. I had a lot of trouble reducing the page width from the default of 1024 pixels (expressed in ems in the template). The answer in the end (emd?) was to adjust the base font size down a notch or two. This worked great in all browsers except IE (so far I have checked Safari, Firefox, and Opera).
The issue in IE is that the page looks way large with IE's Medium font size setting. If you use the View/Text Size setting in IE and choose Smaller, things look good. Given that some IE users have the default IE size set to Smaller I am going to leave things as they are at the moment. If I find an easy auto-size fix for IE then I will implement it.