Lots of info on using Flex Builder to edit, but not so much on debugging. Just taking some notes.
Using FlexBuilder 3 to debug & edit Flash CS3 projects « The Morphic Group
Recently I was working on a project that due to a requirement had to be compiled in Flash CS3. Having spent the last few years exclusively using FlexBuilder I was shocked at the HORRIBLE AS3 editor and debugger in Flash CS3. I quickly tried to figure out how to edit and debug from FlexBuilder 3. I got some help along the way, and wanted to share the process.
