Since current Flash Builder is basically built on Eclipse Galileo, you just have to add the update site for Galileo
In Flash Builder, go to
Help > Install New Software
Click on “Available Software Sites” link, which should open up “Available Software Sites” window. If you don’t have the Galileo update site already configured, add a new Software site. Call it “Eclipse 3.5 updates” and add the URL: http://download.eclipse.org/releases/galileo/
Back in the “Available Software” screen, select “All available sites” for the “Work with” section. In the search input below that, type in PDT and you should see PDT as an item on the search result. Select it and click the next button. Eclipse will now prompt you with a review screen of the packages which are going to be installed. Click next and complete the installation. You may have to restart the IDE for the changed to take affect.
Shown below is the review screen of PDT installation.

PDT Installation for Flash Builder
This resulted in a ton of errors, but most prominently a PHPStructuredEditor failure of some sort. Thanks for the try though. Still trying to solve this problem.
Thanks dude.
Followed instructions and it worked straight out of the box. Only advice I can offer to any others that stumble here is once the 3 items come back from the search for PDT ( in the install new software dialog ), just get the last 2 pdt options and leave the first one. something about accessability module for pdt.
I did this in admin mode, and then once I restarted flashbuilder in normal mode after all was said and done it behaved exactly as I was expecting.
Although admittedly the only reason I’m using flashbuilder is for a legacy project for dad, whereas normally these days I’m using Intellij Idea from jetbrains. Stomps flashbuilder into the ground. little pissed I spent $2900 with adobe to do stuff a $200 app does so much better.
Cheers Jeffery, you made this painless…. now to go back to dealing with a less than perfect environment to make some changes.