Are you using the latest iPhoto'11?
Since the latest iPhoto and Aperture versions you can avoid to import separate images for "edited" and "original" ( in most cases) by importing the complete iPhoto Library (File > Import > iPhoto Library) and not using the the iPhoto Browser.
Importing from the iPhoto Browser always will result in two separate master images for original and version. To delete the copies that you do not want, use the keywords "iPhoto Original", "iPhoto Edited" to define smart albums (File > New > Smart album, keyword is "iPhoto Original") or searches to easily spot and collect the images you want to remove.
Or export either versions or masters from iPhoto.
But the preferred way should be to import the whole iPhoto library. (and delete the events/projects you do not want afterwards)
Aperture 3.3 can now share libraries with iphoto. Merge your libraries, and if you still have duplicates you might want to try out something I wrote for myself. It's Aperture Duplicate Detector available at http://ssoftltd.com/ADD
It won't delete the photos, but will tag them so you can filter based on certain keywords.