Check out review sites
Check out review sites such as this one, DPreview, Steves digicams, etc. and research. Decide what features you need, how many MP, focal lengths, lens speed, battery type, etc. Make a list, see what lines up with your list, make compromises, buy your camera. Both cameras you mention are more than adequate. I am partial to the Canon S2: Excellent zoom range, Image Stabilization, and probably the best digicam movie mode.
Ktixx is correct this post actually belongs in the "Which camera should I buy" forum.
A good photograph is knowing where to stand.
Rule books are paper, they will not cushion a sudden meeting of stone and metal.
Ernest K. Gann-Fate is the Hunter.