I was using Eclipse 3.4 Ganymede until now but wanted to test the new Eclipse 3.5 Galileo with my current Flex plugin installation. The problem is that if you try to install a Flex plugin for the second time, it tells you that it is already installed and you have to choose another install path. Obviously, I don’t want to have a separate Flex installation for each Eclipse IDE so I looked for a solution.
The solution is quite simple when you know what to look for, if you examine both Eclipse installations, you’ll notice that there is an extra “links” folder in one of them where the Flex is installed. You just have to copy the file com.adobe.flexbuilder.feature.core.link into the the new eclipse’s “links” folder (create it if it doesn’t exists).
Or, if you prefer, you can create it from scratch, it is pretty simple as it contains only the path to the Flex plugin installation (path keyword is not mandatory) :
path=C:/Program Files/Adobe/Flex Builder 3 Plug-in
This solution works of course, for multiple Eclipse installations.
(For the moment, there is a bug in Flex compiler, so we have to wait)

Great article! Thanks.
For people who use ZendStudio or maybe other eclipse flavors:
ZendStudio create this link folder but if you just copy from it, it won’t work (eaxmple: to a J2EE flavor eclipse).
Why ? Because there is no ‘path=’ before the path.
You need to edit the copied link file and add ‘path=’