By composition, do you mean sequencing or notation or both? Or something else? What are you trying to do?

I know there's a fair number of open source sequencers, like Rosegarden, that may have Windows versions. Here's a couple of Googled links.

Windows XP 2000 NT ME 98 95 Music Software: MIDI Sequencers [Shareware Music Machine]
Open Directory - Computers: Multimedia: Music and Audio: Software: Sequencers
MIDI/Audio Sequencers - The Sonic Spot

There's probably also notation programs. I haven't tried any, but have used a couple of different commercial packages on Windows and Mac a while ago.

Hope there's something useful.