powershot series have a lot of so call sub series also
Powershot A series (except A300/310 blah blah blah) the lowest end of the powershot
but have a lot of function like a prosumer DC like TV/AV M mode blah blah blah
Powershot S seires 1 class higher than A series , main different i knew is it support Type 2 CF and RAW file
Powershot G series again 1 class hight than S series, prosumer class
ok basically i think powershot series is better than ixus series on the manual, semi-manual mode like TV/AV, scenery mode(good for beginner) but ixus series is small and compact (well its only selling point of ixus of ya so stylish)