Toggle Borders
The accepted way to debug complex table-based HTML pages is to add a border="1" attribute to the <TABLE> element. Toggle Borders is a utility which automates this and more. It is accessed from the context menu in Internet Explorer and will color-code tables, spans and divs for you to see how your website, or a third party website has been layed out. Select Toggle Borders again and the color-coding is removed.
To install, simply unzip the two files, then right click on the .inf file and choose "Install". This will copy the .html file into the Windows directory and register the extension in the Registry. You will need to restart Internet Explorer to see the menu extension.