This goes alongside some sources (linked in the post) and adds some notes that I found necessary. It just relates to installing Flex Builder on a 32bit operating system; for 64bit Linux, there is another article on this site.

1. We need to create a clean environment. Only if you never had Eclipse 3.5 installed on your system, you can jump over this.
   • rm -R ~/.eclipse/org.eclipse.platform_3.5.0_*/
     (Omitting this can cause all Flex perspectives, editors and views to be “hidden” even though Flex Builder 3 alpha 5 for Linux is correctly installed. This happens if a previous failed / wrong installation caused this stuff to be hidden, as the directory deleted above then stores that configuration, seemingly.)
   • Delete your Eclipse 3.5 installation folder and your Flex Builder for Linux installation folder, if you have previous, failed installation attempts.
2. Install Eclipse 3.5 Galileo and Flex Builder for Linux alpha 5.
3. Cure the “path=” issue: open the file {$ECLIPSE_3.5_DIR}/links/com.adobe.flexbuilder.feature.core.linux.link and prepend the content with “path=”. Read more about that issue here.
4. Apply James Ward’s ProblemManager patch (steps 2,3,4,5). A preliminary solution is to switch off warnings in the “project properties -> Flex compiler” settings. I have a more detailed description of the problem to solve here.
5. Apply another patch (Stage 2: steps 5,6,7). The instructions there are for teh Flex Builder 3 alpha 4 build, so the stuff to remove is named differently. But you need NOT to rename the patch files with the new build ID.
6. Update your Flex SDK to Flex 4 beta 2 SDK, and update AIR. Use the stage 3 instructions here and follow the “To use Flex 4 SDK” steps here.