Three long years after first promising customers that it would ship the successor to Windows XP, Microsoft is finally moving ahead on a concrete development schedule for Windows Vista (formerly code-named Longhorn). Vista will be a major Windows release, incorporating a revolutionary UI, a dramatically enhanced Explorer shell, image-based deployment tools, and perhaps most import, vastly improved security. Now that the Vista beta is available, I've had time to evaluate what Microsoft has changed and can more accurately discuss why it's much better than XP. Here's what you need to know about the security improvements in the Vista beta.