Howtogeek posted a guide about installed the new 64-bit version of Adobe Flash on IE 9 beta

You're using the 64-bit version of IE 9 Beta and attempt to watch flash videos, and realize they won't play. Here we look at fixing the problem by installing the new 64-bit version of Adobe Flash.

Getting Started
There are a few things to keep in mind when installing IE 9 Beta with a 64-bit version of Windows 7. First of all it installs both 32 & 64 ? bit versions. Just like you had both versions of IE 8 with a 64-bit version of Windows 7.

  How to Make Flash Work in the 64-bit Version of Internet Explorer