There are some builds floating around the net that claim to be the IE7 Beta 2 Preview release.  These are not offical released builds and are not supported.  You should be extremely cautious about installing such a build.  I would recommend not installing it at all, since you cannot easily trust that the bits have not been tampered with or altered in devious ways.  Furthermore, there might be bugs. 

Stay tuned to the IE Blog for offical announcements of releases.