I know very little about the G5. But I would suggest reading though Steve's review:
http://www.steves-digicams.com/2003_reviews/g5.html
And make sure you pay attention to interface and functionality. Make sure that it really does all you want and can do it in a reasonable way. Settings which are hard to make aren't used as often... which is bad when it's something that you really should be doing to get the quality you want. I believe it is a more advanced than the S200, so that is a good start.
Also, the G5 is a larger and heavier (more than 3 times as heavy) camera than the S200. So you'll have to be willing to trade size for functionality.
Eric