I am using an Apple Wireless Keyboard in OSX 10.6.8. There are apparently several types of keyboard with different keys and key locations so my solutions probably don't apply to your problem. I was assuming similar keyboards and OSX verisons. As a Sage once said: "NEVER ASSUME!"
However, for what it's worth:
APPLE WIRELESS KEYBOARD
Language choice from
System Preferences > language&text > input sources
(Have you been using only Preferences - "Keyboard and Fax" in attempting to change your KB)
FRENCH LAYOUT ---
(uc) >12345678900°_ (dele)
(lc) <&é"'(§è!çà)-
(uc) AZERTYUIOP¨*£
(lc) qsdfghhjklmù (return)
(uc) (ShLoc) QSDFGHJKLM% (return)
(lc) (ShLoc) qsdfghjklmù (UpArrow)
(uc) (Sh) WXCVBN?../+ (Sh)
(lc) (Sh) wxcvbn,,;:= (Sh)
bottom row as shown
You'll notice my " mark is above the "3" so right there we differ. Assuming again though, it seems that your OSX version would be able to read your keyboard and the "language&text - input sources" would be able to offer you the language you need. My OSX 10.6.8 doesn't offer ANSI and ISO but my eMac 10.4.11 does. Strange!
I love being able to switch back and forth between the languages and find I adapt very quickly to the few keys that are in a different place.
I'll sign out now as you can see my situation does not fit with yours and I'm probably taking up your time uselessly. Good luck! ......goldie