After installing FB, you will find Adobe Flash Builder 4.5 Plug-in Utility.exe under <FB installed folder>/utilities. That can be used to plugin FB into existing eclipse. Please let us know if that helps.
I will test this while behind my PC, (at 6 P.M GMT+1).
Thanks for your responsiveness.
You're the man!
I just have to delete the old FB4 link into dropins folder, use the utility, create a new workspace and importing project, and it work perfectly!
The thing that I don't understand is that standalone install does not support eclipse updating, but plugin in FB4.5 on an upgraded Eclipse works...
Sounds strange to me, but I'm very happy to work with one and only one IDE