Two blocks, two transactions, same hash Would a block containing a transaction with an identical hash as a previous transaction be considered valid? That is, if someone made a transaction for generating Bitcoins and solve two blocks with the same coinbase transaction, would the second block using that transaction valid?
The transaction would be valid - there is nothing in the protocol that forbids this. 

This is also the cause of the "duplicate coinbase" bug in the Satoshi client which I discovered a few months ago. If you create a block with a duplicate coinbase and that block then becomes orphaned it will cause the both the original and duplicate tx to be removed from the database.