For all of those Mac users ilife is great because it includes a program called GarageBand. In this program you can use a real instrument or a digital instrument.

ive used garage band before. but on pc i use a program called mixpad. it comes with wave pad and record pad. you can do anything you want on it..there just arnt any digital instruments. oh and one other thing...
its free

garage band is good but it's pretty rudimentary...kind of like imovie is to final cut, garage band is to protools (and such)