Wow, it's been a while since I looked through this thread, but I think everyone needs some reminding...
1) Before you post, look to see if your question has already been asked/answered by someone else
2) For flute, etc. there is no special sheet music - just play the top line on the piano part! However, it is possible for someone to transcribe (or transpose, some people hear different terms), and pretty easily (this example is for treble cleff):
just get out a fingering chart for your instrument
know what key your instrument is in
look at the top line of the piano part
transcribe accordingly. For example, the top piano line (always a "C" instrument, techincally) to, say, the French Horn. If on a piece of piano/flute music you see a C written in the staff, that would be an F on the staff for the french horn - if a french horn were to play what a flute sees as a C, it would be a completely different note since it's in a different key. Here's a cool pic to help illustrate (b/c it's late and I like to explain w/ pics rather than words)
So, if going off of a flute/piano piece and you play the french horn, you take each note down by four positions chromatically... It's all really quite easy - have someone (music teacher, etc) help you if you're still not sure...
Here's more from the same site as the picture above: http://cnx.org/content/m10672/latest/
* Common Transposing Instruments
Clarinet is usually a Bb instrument. The most common clarinet sounds one whole step lower than written, so parts for it must be written one whole step higher than concert pitch. Like French horns, clarinets used to come in several different keys, and clarinets in A (with parts that are written a minor third higher) and other keys can still be found.
*Alto and Baritone Saxophone are Eb instruments. Parts for alto saxophone are transposed up a major sixth. Parts for bari sax are transposed up an octave plus a major sixth.
*Tenor and Soprano Saxophone are Bb instruments. Parts for soprano sax are written a step higher than they sound, and parts for tenor sax are transposed up an octave plus a whole step (a major ninth).
*English Horn is an F instrument. Parts for English horn are transposed up a perfect fifth.
*Trumpet and Cornet can be in B flat or C, depending on the individual instrument. B flat is the more common key for cornet. If you are writing for a particular player, you may want to find out if a C or B flat part is expected.
*French horn parts are usually written in F these days, up a perfect fifth. However, because of the instrument's history, older orchestral parts may be in any conceivable transposition, and may even change transpositions in the middle of a piece. Because of this, some horn players learn to transpose at sight.
*Alto flute is in G, written a fourth higher than it sounds.
* Tubas and euphoniums may also be transposing instruments. Some tuba and euphonium parts are written as bass clef C parts (sometimes even when the instrument played is nominally not a "C instrument"; see below for more about this). But in British-style brass bands, BBb and Eb tubas (called basses) are written in treble clef. The BBb is written two octaves and a major second higher than it sounds, and the Eb an octave and a major sixth higher than it sounds. in France (and in the case of parts printed in France), you find Bb euphoniums (calles basses or petites basses) written for in bass clef transposing by a major second, and bass tubas (called contrebasses) in Bb written for in bass clef transposing by a major ninth. If you are writing for a particular group or player, you may want to check to see what kind of instrument is available and what transposition the player is comfortable with.
Some transposing instruments do not change key, but play an octave higher or lower than written.
*Guitar parts are written one octave higher than they sound.
*Men's voices, when given a melody written in treble clef, will usually sing it one octave lower than written.
*String Bass parts are written one octave higher than they sound.
*Piccolo parts are written one octave lower than they sound.
*Contrabassoon parts are written one octave higher than they sound.
*Handbell and handchime parts are written one octave lower than they sound.