This is very useful. It lets you see just how messed up IE’s internal model of where elements are is… A good tool indeed, excellent addition to the web designer’s toolbox. By the way, it does in fact work on Windows 2000, in case you were wondering. 🙂

It’s pretty much like the IE version of the Firefox Web Developer Toolbar extension.

Download details: Internet Explorer Developer Toolbar Beta

Overview
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 800×600 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.

The Developer Toolbar can be pinned to the Internet Explorer browser window or floated separately.