I've gotten a lot of questions about IE 8, but there's not a lot out there. Nothing is set in stone yet, but here's what Microsoft is examining for the IE 8 browser window UI now.
First, IE 8 will fix the silly toolbar issue in IE 7, where the Home button is moved over to the right side of the window; it's back next to Back and Forward where it belongs. ("Menus are more discoverable" in Microsoft-speak.)
IE 8 will utilize a Quick Access Toolbar, just like Office 2007. This will let users "expose any command at the top level" of the browser "outspace" and give more room for tabs.
Microsoft briefly examined an Office 2007-style Ribbon UI for IE 8 but found it to be far too tall. The tallness of IE's top-level UI became an issue with IE 7 even though IE 7's UI isn't that much taller than that for Firefox or IE 6. The Ribbon would have really made it too tall.
Here's a mockup of the current internal design:
I mocked this up in Paint, but the basic browser window is obviously very reminiscent of IE 7.