Free music programs?
One I can think up of is PXTone, the program Pixel made to make the music for Cave Story.
http://www.tigsource.com/2010/12/26/gry ... ne-manual/
The demo of Fruity Loops Studio is free and fully-functional, minus a save feature.
So you can do anything you want with it, you just have to finish the song in one go, or just... not exit the program till you're done.
Likewise, REAPER has a free, infinitely-renewable trial, but it's much harder to figure out. Basically, when the 30 days are over, uninstall REAPER (don't worry, all of your project files are still there), and just re-download it. And continue.
For the making of 16bit Sega-Genesis music, I recommend the freeware tracker TFM Music Maker. The website is down right now, so you'll probably have to look elsewhere. If you never used a tracker before, it's hard to get in to, but once you learn the ins and outs of the system it's quite useful and powerful. Not very strong percussion (as everything is based off the YM25125 chip, and there is no sampling/PCM to speak of).
In the same tone, the free tracker FamiTracker can accurately recreate the sound of the Famicom chip, including its extensions, VRC7 and N106!
You can go even more old-school with the .MOD open-source MilkyTracker, which is more in line with the C64 sound (though this is only off of impressions, don't quote me on that!).
That's about all I gots to offer. Should be a good enough place to start out.