I recently had Ethereum on Windows (Ethereum Wallet) and Mix. Later I copied the whole ethereum folder on Windows to a cold storage and installed Ubuntu on the machine.
My question is how do I import those windows ethereum files?
all i had to do is copy the Ethereum folder contents from the old OS into the the hidden .ethereum folder on Linux. Everything will sync up automatically after you use the geth updatedb command
I'm unsure if you are attempting to copy the blockchain (so you don't have to resync?) or import your accounts. I'm not sure how the chaindata is set up on Windows vs Linux, but if you just want to see accounts, you can check out the answers on this thread.