Can I open iPhoto 7.1.5 library with aperture 3.4.3?
Is there any other workaround, such as exporting my iPhoto 7.1.5 library to some other format and then importing such format to Aperture 3.4.3? I will be grateful for any help with this odd situation.
How many photos are you talking about? If you have huge iPhoto Libraries, and have invested much work into organizing and adjusting your photos, you really will want to import your iPhoto library as Library. This way you will transfer your work, not only your photos.
If your library is small, and you do not mind to do all the organisation and adjusting again, you can export your photos from iPhoto 7 - create a folder in your "Pictures" folder and export your photos from iPhoto to this folder, one event at a time as separate folders of image files. You can either export the original images or the edited versions. If you have done much editing, export both, to save your originals. Then import these folders of image files into your Aperture library.
But if you have huge libraries to transfer and many years of editing to preserve, the sensible thing to do would be to invest into iPhoto 9.4.3 and to upgrade your iPhoto libraries to the new unified format. You will not only save your edits and library organisation, you will also save plenty of disk space, for you can import the edited versions and originals as master-version pairs and not have to deal with duplicates.
When did you buy Aperture? Do you have a serial key for Aperture, that can be used with the Aperture Trial version? Then you might consider to reinstall Aperture 3.2.4 from your backup (rename your current Aperture version while you are doing that) or to download the Trial and try to import your iPhoto library into a new Aperture library. Earlier Aperture versions could import older iPhoto libraries, but will import two image files (Version and original) for each iPhoto image. So you will end up with plenty of duplicate images that you will have to organize. (A link to the Trial is here: Aperture 3.4: May quit unexpectedly on launch after updating).
As I said - to invest into iPhoto '11 will have a lot of advantages.