Bit of a hack
as there isn't an official Mac keyboard layout that does it, like the UK PC keyboard (the Mac variations usually consist of adding umlauts & being QWERTZ etc in foreign countries, I've never seen one with the punctuation swapped)

This page seems to be what you're after though.

Edit: doing something in a manner other than what Apple decree you WILL DO, will result in a midnight raid by Cupertino stormtruppen. You have been warned.
(Son of Sam-i-am We're all as mad as hatters here, Mon 12 Jan 2009, 12:09, Reply)