Today, I am happy to announce immediate availability of Microsoft Application Virtualization (App-V) 4.6 Beta. At TechEd EMEA we announced our commitment to ship the next version of App-V in H1 2010. In March of this year, as part of the MDOP 2009 launch, we indicated that the development of App-V 4.6 was underway. Today, we have reached a major milestone and are a step closer to our goal. This will be the first version of App-V to support both x64 and x86 Windows platforms. The primary focus of this release is to enable App-V to take advantage of 64-bit Windows platforms including Windows 7 and Windows Server 2008 R2. We’ve also made some improvements in the App-V Sequencer such as simplifying the workflow for creating virtual applications and adding the ability to sequence true 64-bit applications, a first to market! For customers running Windows XP or Windows Vista, you can also use App-V 4.6 Beta and take advantage of the support for Office 2010, 64-bit platform support and additional features in the release.

Source: http://blogs.technet.com/mdop/archive/2009/07/30/app-v-4-6-public-beta-now-available-for-download.aspx

Be sure to also read this article by Tim Mangan that already has a review of App-V 4.6: http://www.brianmadden.com/blogs/timmangan/archive/2009/08/04/microsoft-beta-for-app-v-64-bit.aspx