Some card like Creative's SB Live series comes up with bundled firm ware to do this. Creative's Virtual keyboard...
Some Apps like Cakewalk also give Virtual Piano to do what you want.
Anyway, using PC's keyboard as "piano like" keyboard to be MIDI controller is quite not that wise. You may find alot of cons once you've tried. It doesn't record velocity (key pressure level), after touch, etc... I think having a cheap MIDI controller like Studio logic / Fatar / Roland PC MK series would be better.
Anyway, using PC's keyboard as "piano like" keyboard to be MIDI controller is quite not that wise. You may find alot of cons once you've tried. It doesn't record velocity (key pressure level), after touch, etc...