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Hypothetically you can try downloading all the v1.6 files then installing it (remember to import your old database in the new database before installing). Again do this on a backup copy non production server.
You won’t have any of your customizations or extensions installed. But once you verify its working you can begin to import those in.
Though i had 1.6 already but switched to 1.5 when i installed a Rockettheme http://www.rockettheme.com/magento , those are all 1.5.
When manually installed one of these themes, images did not showed up.
Products i exported via csv in 1.6 (beta) but now with 1.5 i can’t import them.
Is there maybe an extension key i could try? And next i might go back to use the 1.6 install and try again to install the theme instead of the other way around.