Its available for download now

Existing beta1 users should be getting software notification upgrade prompts shortly.

Enjoy the fast upgrade experience from Microsoft AntiSpyware beta1, and no reboots required :)

Checkout the FAQ http://www.microsoft.com/athome/security/spyware/software/about/faq.mspx

 

What is Windows Defender?

Windows Defender (Beta 2) helps protect your computer against pop-ups, slow performance, and security threats caused by spyware and other unwanted software. It features Real-Time Protection, a monitoring system that recommends actions against spyware when it's detected, and a new streamlined interface that minimizes interruptions and helps you stay productive.

 

Improvements in Windows Defender (Beta 2):

Enhanced performance through a new scanning engine.
Streamlined, simplified user interface and alerts.
Improved control over programs on your computer (using enhanced Software Explorer).
Multiple language support with globalization and localization features.
Protection technologies for all users, even those who do not 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.
Information about the most recent spyware threats that Microsoft has identified.