I've been struggling with this dilemma for a while now: I have backed up my entire hard drive about three times and on each backup I have my iPhoto library. Most times I backed up because I was traveling or was in a hurry and didn't think about how to get some of the info off of the hard drive. The last time I did a clean install I decided that the 60 gig hard drive in my laptop was just not enough, so now I keep all my music and photos on an external 350 gig drive which works great, except that my photo library reaches only as far back as a few months ago. I got my first digital camera about seven years ago and would love to get all those pictures back. If you've tried to look through the folders iPhoto makes, it makes this task daunting. Everything is organized by year, month and date and thumbnail photos are everywhere. Simply dragging an old library will just not work well.

I learned about how you can load iTunes and hold the option key to select a library, so I decided to try this with iPhoto. Low and behold it worked !

Here are the steps to merge your old library and current library:

1. Drag iPhoto to your dock (if it's not there already)
2. Hold Option and click iPhoto
3. It will prompt you to choose a library, select your old one (the entire folder labeled iPhoto Library)
4. If it was made in an older iPhoto, it will ask you to upgrade the library
5. At this point you can access your old library, with albums in tact. Might be a good time to select only ones you want to bring into your current library since this technique will lose the old album data (of course you could drag each album into a separate folder on your desktop one by one)
6. Create a new folder on your desktop, drag the photos you want to bring over to this folder
7. Quit iPhoto, restart and hold Option again, and select your normal library
8. Create a new album called something like "Old Photos"
9. Drag the folder you recently made on your desktop to this new album

If you've got iPhoto '08, losing the album data isn't as bad because it automagically sorts the photos by date