It's easy to debug HTML or CSS code in browsers like Opera or Firefox, because they provide their own tools. There is a Dragonfly for Opera and Firebug for Firefox. But what about IE?
Well there is an option to use firebug light version and inject it right into current page to have almost same functionality like with Firebug in Firefox.
Just open website you want to debug. Delete address which is displayed in address bar and copy this code and press enter.
Or just add this link to favourites in IE and use it on any page you want to debug
More information on Firebug lite