iPhoto is known to lock up if you try to delete a large number of photos at a time. Here are a couple of ways to get out of the predicament you're in:
1 - go into iPhoto's General preference pane and uncheck the Show item counts checkbox:
and then try emptying the iPhoto Trash bin again.
2 - If that fails and you don't use the Rating stars you can do the following: select all of the photos in the trash and Control-click to bringup the contextual menu. There will be the 5 stars for the ratings. Select either 5 or 1 to apply that rating to the photos.
Next create a smart album with the criteria:
selecting the number of start you applied to those in the Trash bin.
Move the photos from the Trash bin to the Library and the Smart Album will immediately be populated with those photos.
You can now select about 100 photos or so at a time and use the Command+Option+Delete key combination to move them back to the Trash bin and empty it. Repeat with groups of about 100 or so photos till they are all deleted. Then delete the Trash bin in the Dock to completely remove them from your hard drive.
