Hi GiantsFan,
I had a quick look in the main iPhoto prefs and couldn't find anything, but i managed to find the reference in the preference file. So, you should be able to stop the automatic importing of duplicates by opening the Terminal and typing
Code:
defaults write com.apple.iPhoto ImportDuplicates 0
This just changes the entry in the prefs file located in
SystemDisk/Library/Preferences/com.apple.iphoto.plist
Hope that cures the problem,
ac2102