I use Muscript:
http://www.pjb.com.au/muscript/
But it is not very user friendly. I then use GhostScript and/or GSView
http://sourceforge.net/projects/ghostscript
http://www.cs.wisc.edu/~ghost/
to view the PostScript output that MuScript makes. Then I "print" it using PDFCreator:
http://sourceforge.net/projects/pdfcreator
What PDFCreator does is it sets up a virtual (bogus) "printer" - anything you print here gets saved as a PDF (or JPEG, or a handful of other formats).
I suspect you'll want to use something a little more user friendly, and that has a graphical user interface (GUI), like Lilypond:
http://www.gnu.org/software/lilypond/lilypond.html
If Lilypond doesn't write PDFs (don't know; I've not used it), you can use PDFCreator.