How to import an old iPhoto 09 library to iPhoto 11?

I have found an old iPhoto 09 library on a back up folder and I want to import its content to my newly purchased iPhoto 11. Is this possible? If yes, how is it done?

By the way: I tried to import it through iPhoto 11 by SHIFT-CMD+I and then navigating to the old library but it was grey and therefore not possible to select.

Open the old library directly by holding down the [option] key while starting iPhoto. iPhoto will then allow you to browse to the library location (use the "Other Library" button) and should update it automatically to iPhoto '11 format. You may want to back it up first

Close iPhoto and restart holding [option] once again, make sure the active library is your current (new) one. Try reimporting the old library now. It might still be greyed out in the file picker but double click it anyway, it should import.