i have already downloaded the iPhoto 11 but when i try to pull up an old photo file its saying i need to prepare the library ? HELP !!!!

Well prepare the Library. I'm sure the exact message you get will have a clue...

Just a guess since you provide no information to let us help you - if you old library is from iphoto '08 9 (version 7.x.x) or earlier then you need to download and run the iphoto library upgrader before launching iphoto '11

LN

I upgraded Yosemete my Iphoto was upgraded I chose the wrong library, apparently I have more than one, so I followed the directions on the upgrade and no luck I cannot open my Iphotos unless I go through the search mode and find the file, otherwise it will not let me switch between libraries...So frustrating on a mac less than a year old GRRRR!