Transposing tablature at sight, or playing a keyboard instrument while reading tablature, are not impossible. I find the first tricky, and the second remarkably easy, as long as the tablature is French. It all depends on how you learned the lute in the first place. If you started with tablature, you are likely to see the letters only as positions on the fingerboard, and transposition will be well nigh impossible. If, on the other hand, you started with staff notation, those tablature letters are more likely to represent pitch, making transposition or playing the music straight on a piano much easier.
Roman's point about temperament is a bit of a red herring, because the evidence points towards equal temperament being the norm for lute and viols by the beginning of the 17th century. Stewart McCoy To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
