I think I know what your problem is, although hard to explain.
I'm guessing no fixed font sizes for those different areas are setup in the stylesheet of the bluetabs themepack. Probably the Font Size setting in IE is set to 'Smaller', probably as soon as you set it to 'Normal' it will look similar to the Netscape screen.
(Naming could be different cause I only have a Dutch version of IE on my pc)