Briefly.. (As a guide only...)
CAT I - 200ft and 550m Visibility
CAT II - 100ft and 300m
CAT IIIa - 50ft and 200m
CAT IIIb - Below 50ft (e.g. 744 and 75/76 have no decision height, they decide once on the ground)
Types
CAT I - any basic aircraft in the world with an ILS receiver and a half competant pilot.
CAT II - 146, some OLD 737-200
CAT IIIa - 737-200ADV, all newer 737, Avro RJ
CAT IIIb - 747, 757, 767, 777, A320 etc etc
Cough