We want to merge two magento installs into one, combine two different product ranges and their respective websites into one backend. All we need is to combine the products and websites of both installs. (And I realise that "all we need" is more complex than it seems at first sight.) Old orders can still be opened in the old install, old customers with login will loose their account on one install.
Websites, categories, attributes, bundled products and more have to be handled as well. Product images, product stock... Some of these will probably be done manually.
I would like to get an idea of what else has to be handled, what I'm forgetting here. I would like to know if you have done this before, successfully, and how you did proceed.