A lot of people have had questions about whether you can use the Flex 2 Framework classes / controls (everything in mx.*) within an ActionScript 3 project without using any MXML.
You can definitely do this, and we have posted some info on the labs wiki that shows how (written by Gordon Smith).
You can view the info here.
You can download Flex Builder 2 and ActionScript from labs.macromedia.com.