If you think you’ve found a bug in the Flex SDK or in Flex Builder (any versions), you can file a bug in the public bug base at http://bugs.adobe.com/flex/. You can also use the same URL to file enhancement requests for features that you want to see in future versions of the SDK or Flex Builder. Similarly, there is a Flex Wiki set up at http://bugs.adobe.com/confluence/display/ADOBE/Home which outlines the Flex planning process, notes on how to use the public bug system (how to create accounts, searching for bugs, voting on bugs (very important!), as well as frequently asked questions, and a few other gems).
You can find out more about the open source Flex SDK framework at http://opensource.adobe.com/wiki/display/flexsdk/Flex+SDK. The latest official downloads for the Flex SDK or Flex Builder 3 can be found at http://www.adobe.com/go/flex3_sdk, or, you can download the latest milestone release builds, stable builds, or nightly builds of the Flex SDK from http://opensource.adobe.com/wiki/display/flexsdk/Download+Flex+3.
Want a free version of Flex Builder 3? Check out https://freeriatools.adobe.com/ and see if you qualify!