Thanks for the feedback. Unfortunately it doesn’t help at all. Even in FireFox my site’s layout is now all wrong. In IE7 it’s a complete mess with the footer appearing directly below the top menu bar. For now I’m going to have to undo the changes to the css files as it is a production site. I’m going to reinstall the theme from scratch and will report back.
UPDATE: I returned everything to default install (from step 1 to 5). I then made the recommended breadcrumbs style changes to the boxes.css file (Step 4) and left everything else as original. For some reason this solved all my problems. In IETester IE6 and IE7 display all pages correctly with no layout problems and the other browsers’ layout is also fixed. Very strange but it seems to have worked.