The IE Developer Toolbar provides several features for deeply exploring and understanding Web pages.

– Explore and modify the document object model (DOM) of a web page.
– Locate and select specific elements on a web page through a variety of techniques.
– Selectively disable Internet Explorer settings.
– View HTML object class names, ID’s, and details such as link paths, tab index values, and access keys.
– Outline tables, table cells, images, or selected tags.
– Validate HTML, CSS, WAI, and RSS web feed links.
– Display image dimensions, file sizes, path information, and alternate (ALT) text.
– Immediately resize the browser window to 800x600 or a custom size.
– Selectively clear the browser cache and saved cookies. Choose from all objects or those associated with a given domain.
– Choose direct links to W3C specification references, the Internet Explorer team weblog (blog), and other resources.
– Display a fully featured design ruler to help accurately align objects on your pages.

http://www.microsoft.com/downloads/details.aspx?FamilyID=e59c3964-672d-4511-bb3e-2d5e1db91038&displaylang=en