They say that IE7 will be a tabbed browser. It will also feature support for international domai name (IDN), transparent Portable Network Graphics (PNG) and a built-in news aggregator.
Among the myriad security enhancements Microsoft is expecting to include in IE 7.0, according to partner sources:More details at Microsoft-Watch
reduced privilege mode becomes the default; no cross-domain scripting and/or scripting access; improved Secure Sockets Layer (SSL) user interface; possible integration between IE 7.0 and Microsoft's Windows anti-spyware service, which currently is in beta.