Apple Menu -> System Preferences -> Keyboard & Mouse -> Keyboard Shortcuts
Then click on the bottom checkbox.
TAB now moves between checkboxes, buttons, and so on.
I can't believe that isn't the default. What were they thinking?
(This announcement was brought to you by Unix Wonks That Now Use Macintoshes)
Nope--this still doesn't fix this for me. It allows me to use the keyboard in *some* things but... go to a page where you have to log in using Apache authentication--try and tab to the "remember this logon.." It still requires a mouse.. :-/