Transposing instruments

[Helge Kruse]

I am transcribing an autograph with an arrangement for a small 
orchestra. There are two transposing instruments: Clarinet in B and 
French horn in F. The piece itself is set in g minor (some parts also in 
g major).

The original score begins with this picture:

oboe = \relative c'' { \key g \minor d16 d8. ~ d4 }
clarinetB = \relative c'' { c16 c8. ~ c4 }
hornF = \relative c'' { d16 d8. ~ d4 }

\score { <<
  \new Staff { \oboe }
  \new Staff { \clarinetB }
  \new Staff { \hornF }
>>
  \layout {}
  \midi {}
}

besides some other voices. I know the name "Clarinet in B" but honestly 
I don't know what this means. Which pitches should I get from these notes?
How can I set this with Lilypond so that I can also create a MIDI file 
with correct pitches? I would like to have the MIDI file for acoustic 
error check of my transcription.

How can I use \transpose and \transposition to get both a nice looking 
PDF output and a useful MIDI file? I assume that the music definition 
will include the \key g \minor for all voices and the transpose will 
change it and removes the flats. But I didn't get it in the last hours.


Regards
Helge