You can compose music using Mod2PSG2, various MIDI convertors, XPMCK, and various others. If all you want is some samples then I suggest you grab some VGM files and Winamp and play with the channel controls.
I did find a software for Mac to listen to the vgm files (Audio Overload by Richard Bannister, the same dude who made smsplus which is the emulator I use to play da games. Halfway there! Now just gotta find one to compose... :-)