Finale, I have used it back in high school and I find it to be the easiest program on the windows side, it also works on mac well= the best one to use for midis.

Besides Piano Keyboard, you can also plug in an electric guitar for input or think it out... It is quite easy to compose in once you have a feel for it.
There's also the awesome included OS X- SoundRecorder on Mac side which will record anything, I use it to record voice onto the former midis converted into mp3s for composition demos.