SERIOUS iPhoto problem, many photo's 'corrupt'

Ok I have a really serious problem with iphoto. Every once in a while I will try to double click on a photo to view it but I will just get a white screen with the spinning thing like on startup. Usually I just delete the photo because it hasn’t happened to any important photo’s till now. All of the pics I took of my dog as a puppy are screwed up (as well as many others) The same thing happens to them. You can see the thumbnails but nothing more. I tried holding down apple, option control shift or whatever the combo is on iphoto startup and rebuilt the iphoto library but the same thingkeeps on happening. I tried dragging the thumbnails to the desktop and opening them in preview and I got this message “couldn’t open the file. It may be corrupt or a file format tht preview doesn’t recognize” I don’t know what to do. I really need these photo’s. PLEASE HELP. oh an i have already done fsck, reset pram, repair permissions and all that jazz nuthin works. i'd like to know how to prevent this from happening and more importantly fix/repair the 'corrupt' photos because they are the only coppy of them that i have

all of the photo's were taken with a sony cybershot 3.2 megapixel camera and uploaded straight into iphoto