Just to give you a quick model run-down:
172 Ph1 (often called "Mk1 172") 2000-2001: pre-facelift hot version of Mk2 Clio. Some say it looks meaner; most are silver; has all the toys bar xenons. Said to be the fastest, although no significant weight advantage... probably due to mileage sensitivity of engine; early ones have alloy bonnet. From about £5k upwards.
172 Ph2 ("172 Mk2") 2001-2004: facelifted hot version of Mk2 Clio. Subtler than original 172; adds automatic xenons and auto wipers; 6-CD stack on some; much improved dashboard and interior plastics; bigger 16" wheels (later 15" version of same wheel used on lesser models, to much annoyance!). No power change, but more torque developed at lower revs. Is the most common model on used market: from £7k upwards.
172 Cup 2002-2004: stripped out version of Ph2 172. Deletes air-con, climate, leather, ABS, auto xenons, auto wipers - but adds stiffer suspension set-up, different wheels and blue interior touches. Loses 80kg, taking car down under 1000kg (same as old Mk1 Clio 16V and Williams). Only available in Mondial Blue, bar 75 late silver ones. Climate/air con available as option on later models. No other mechanical changes (unlike old Williams). Approx £7k upwards.
182, 182 Cup and 182 Trophy: 2004 on. Hot versions of Ph3 Mk2 Clio. Another 10bhp from 172 engine, twin rear exhausts, new wheels and colours. Otherwise same in looks and details to Ph2 172. "Cup" suspension option available on 182; Cup model loses equipment as 172 Cup, but keeps ABS; Trophy is run-out special edition. From about £9.5k upwards.