MuseScore is a free alternative for Windows & Linux:
[
musescore.org]
There are other options available as well, but I'm not sure if they have Windows versions. The most well known of these are Lilypond, with either the Denemo (GTK/Gnome) or Frescobaldi (QT4/KDE4) front ends, or Rosegarden. Rosegarden will also do MIDI sequencing for you as well.
Adieu! (Or is that, "Adoughnt"?)
PCGuyIV