Rename your current library to "iPhoto Library-corrupt"
Put your last backup into the Pictures folder.
Launch iPhoto and see if the backup opens fine.
You now have a working library.
Now you need to get the newest imports from the corrupt library out. No problem.
Check in the open iPhoto the last date of imported images on your backup.
Now navigate the corrupted iPhoto Library and drag the numbered day folders of the newest imports to the desktop. You can rename these folders to the correct date of capture if you wish.
You do not need the Originals folders or the thumbnail folders, just the images in the date folders.
Drag these folders inot the open library window to import them.
check out the screenshot to help you figure out where everything is.
It is organized by Year folders. Inside the Year folders are Month folders. Inside the Month folders are the days of the Month. Inside the day folders are the photos you took on that day. If you imported video clips and RAW files on that day they will be in an Originals folder. If you have edited any photo imported on that day, the original will be in that folder also.
I have a similar problem with iPhoto 5.0.4: I have 21,000 in my library and yesterday iPhoto ceased fully opening and all I get is a spinning wheel. I can relabel my original library, generate a new library and inport the photos again, but I was rather hoping for a solution that didn't fix me to my Mac for days on end. So far I have generated a new temporary library - all works well. I have reinstalled iPhotos - all works well. So the problem appears to be with my original iPhotos library. Problems started after I quit after uploading images to my .Mac homepage. Any ideas on a way forward?