The above is true, but ONLY if the music or videos your playing is was recorded in 24bit. In other words, if you have a 24bit sound card and the stuff your listening to was recorded in 16bit, then you aren't going to hear a difference. If it is 24bit, then you will notice a difference.
EDIT: Its like having a Hi Def TV but without Hi Def channels (you need those channels to really see the difference.