Is there some program, GLP, that can simulate musical instruments?
best place to try your luck is(in fact there are tons of apps):
tuto bem?
if you want realism, use samples, and a good program to make music out of samples is jeskola buzz, or a slightly more user friendly one is taureg 2. both of these come equipped with both trackers ( for playing back samples at various pitches in a sequence ) and a variety of internal synthesizers, and drum machines. taureg actually has only one of each, but you may want to start with taureg and when you want something more powerful, but that takes more time to learn, get jeskola buzz. also if you have a soundblaster or soundblaster compatible soundcard, you can use ‘soundfonts’ in conjunction with midi. in a second I’l get you a URL with a list of many such freewares.
http://www.hitsquad.com/smm/ <edit> lol same URL hehe