Things have changed between Flash Builder 4 beta and Flash Builder 4 (final), so I figured just as well update my old blog post.
http://renaun.com/blog/2010/03/31/416/ tells the story. Here's the steps I had to do:
1. In Flash Builder, go to Help -> Software Updates...
1a. If you get a "No Updates Found" popup, press "Yes" to open "Available Software Sites". Note that both Flex Builder 3 and 4 Beta used to have some sites by default. Whatever, we'll just add one ourself.
1b. In "Available Software Sites", click "Add" on right side.
Add "Galileo" as the "Name:".
Add "http://download.eclipse.org/releases/galileo" as the "Location:".
Say "OK" :)
Step 1 - same
In Adobe Flash Builder 4, go to Help -> Install new software.
Step 2
In the first box ("Work with", pick the "Galileo".
Step 3
Below the search results, un-select the "Group items by category".
Step 4.
Among the search results, select "Eclipse Java Development Tools" and click "Next". Click "Next" again. Accept the license agreement and click "Finish".