I recently downloaded the editing software Aperture 3. I tried to import directly from iPhoto and whether i select one or two files they all duplicate.
iPhoto is like Aperture a database and digital media management system, that keeps the original master image files, to be able to undo edits and to revert to the original image. When you import from iPhoto to Aperture, then Aperture will try to save the original master image file in addition to the edited version; so for edited iPhoto images you will get two imports: the original master and the edited version.
i cannot see a way to prevent this?
What is your iPhoto Version? If it is the most recent iPhoto '11, then there is a better way to import from iPhoto. Don't import single images from the iPhoto Browser, but import the complete iPhoto Library at once. If you import using the Aperture File-menu
File > Import > iPhoto Library
then Aperture will import most of the images as a master-version pairs, with the iPhoto master image file as the master and the edited version bound to the master. This way you will see only one image in Aperture, and you will only need the disk space for one master image file. That would be the most efficient way to import from iPhoto. Also this way Aperture will recreate the structure of your iPhoto library with the events mapped to projects, and preservin the folders and albums.
If your iPhoto version is older, there is no help for it - Aperture will import the master and the version as separate images with separate master image files, but these images will be tagged by keywords "iPhoto original", "iPhoto edited"; so you can filter the imported images by searching the keywords and easily delete the redundant images you do not want.
As a work-around export either the masters or the edited versions from iPhoto and import only one set.