Software to play around with composing music?

[Adam Funk]

Can anyone recommend some software that will let me throw notes on a
score and play them back?  All the MIDI-related stuff I've seen seems
to relate to using external MIDI devices --- I'd just like to compose
(using the term very loosely) and play the score through the normal
sound output and to any normal sound file format (e.g. wave, MP3,
Ogg).

Thanks,
Adam