Which version of Flex Builder, 2 or 3? If it's the release version of FB 3 you will have the latest hotfix already, if it's FB2 then see if this file exists:
>C:\Program Files\Adobe\Flex Builder 2 Plug-in\Flex SDK 2\flex-sdk-description.xml
If it doesn't then I believe that means you don't have any hotfixes installed. If it does, you can open it and see which hotfix has been applied.