http://www.microsoft.com/athome/security/spyware/software/default.mspx
++++++By design, the final release of Windows Defender removes Windows Defender (Beta 2)++++++
Windows Defender features
• New option to display Windows Defender system tray icon even when there are no pending actions needed.
• Enhanced performance through a new scanning engine.
• Streamlined, simplified user interface and alerts.
• Improved control over programs on your computer with enhanced Software Explorer.
• Multiple language support with globalization and localization features.
• Protection features for all users, whether or not they have administrator rights on the computer.
• Support for assistive technology for individuals who have physical or cognitive difficulties, impairments, and disabilities.
• Support for Microsoft Windows XP Professional x64 Edition.
• Automatic cleaning according to your settings during regularly scheduled scans.
Microsoft encourages all Windows Defender (Beta 2) users to download and install Windows Defender.
Known issues
• By design, the system tray icon for Windows Defender does not appear if you do not need to take action.
• Windows Defender might prompt you to remove some peer-to-peer (P2P) file-sharing programs. If you choose to remove such a program, Windows Defender deletes all the contents of the Program Files folder associated with the P2P program. Because some P2P programs store downloaded files in a default folder under Program Files, this might remove all files you have downloaded through the file-sharing program. For example, KaZaA stores .exe and .dll files at C:\Program Files\Kazaa. Downloaded files are stored at C:\Program Files\Kazaa\My Shared Folder. If you use Windows Defender to remove KaZaA, all files and folders under C:\Program Files\Kazaa are removed. If you have installed any P2P file-sharing programs, it is a good idea to back up your downloaded files before you run Windows Defender.
• You do not need to remove other antispyware or antivirus programs to run Windows Defender. Other programs or Windows Defender might prompt you to allow or block an action, but there are no other known incompatibilities between Windows Defender and other antispyware or antivirus programs.
• Windows Defender offers only limited Group Policy settings. The final version of Windows Defender will include administrator (.adm) files so that you can configure those limited settings in Windows Defender through Group Policy.