VTEC is just Honda's variable valve timing and lift system. It uses different cam lobes for more power at high rpms while using a lower lift/duration profile at low revs for better fuel economy/torque.

Try searching google or wikipedia, I'm sure you'll find a good number of write-ups.

The Prelude forum might give you better results but I know the 3rd gens didn't have VTEC, it was available over here on the 4th gen starting in '93 but only on the VTEC trim level.