Hi Rich,
If you are on a PC, you should install WAMP, its free and will allow you to view your PHP pages as they are meant to be.
The reason that some of your php pages were viewable and some not may be due to the fact that your early php pages may not have contained any actual php code. Just regular html?
If you eventually upgrade to CS4 then you would no longer need WAMP as the new Live View in CS4 will do the same thing.
Brad