All the above info is to prevent other applications or system to overwrite your photo files, if unexpectedly iphoto suddenly decided they had been trashed, i.e. "over-writable"... I suggest for maximum security:
Do not try repairing the permissions or anything on the disk (YET).
Start up on another computer running same version of iphoto, then link up with Firewire and in TDM (Target Disk Mode: More info:
http://docs.info.apple.com/article.html?artnum=58583). Then try importing all photo files directly in iPhoto from the "active" computer (using your "sick" computer as a HD)...
If no avail, then scan the HD with the above listed software...
When files have been recovered try repairing permissions with the Apple "disk utility" application...
I got into a similar mess with iTunes... importing all songs on a second computer did the job... never understood what went wrong... never did it again, but then again I do have a back-up now, so it probably won't!