Sibelius is massively expensive. Not free.
For free music making, I can suggest several things.
MuLab Free http://www.mutools.com/downloads.html (I haven't used it per se - I used MuTools Luna for a while. It wasn't bad, although I'm still using Muzys 3 still for my main work, probably just out of habbit more than anything).
Ardour is very good, if you're running OSX or Linux. LMMS doesn't look too bad either. Unfortunately for you most the comprehensive free DAWs are for Linux (Ardour, Rosegarden, Qtractor etc...).
For VST instruments, it's always worth browsing http://www.vst4free.com/ and KVR Audio.
If it's just pure audio you're after, you can't go too far wrong with Audacity.
I hope this helps a little bit.

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