IEBlog : IE7 Has Tabs: From the IE blog:
"Yes, IE7 has tabs.
In general, I think tabs are a great idea. I liked them a lot in Office dialogs and in Excel in the early 90's. (I used to work on Office, and I admit we almost added tabs to Word at one point.) I like them in Visual Studio. I think, as an industry, we have a ways to go in refining the experience, consistency, and value of tabs.
The main goal for tabs in our beta release is to make sure our implementation delivers on compatibility and security. The variety of IE configurations and add-ins across the Internet is tremendous. We want feedback on how it works with add-ins that you run (or have written), with the sites that you visit, and with the line of business applications, accessibility tools, management and development tools that you run."