Yes, F is the same as F Major...I'm not too sure exactly what you meant but I think I have an idea...It's not really a case of being interchangable, just what ever you prefer to play...I play a full barre for example, my father will some times play only the top two string, e and B.
Now, Hoxman...Basically there are only really three chords on the guitar...E, A and D... So, if you start the root on the 4th string, it's the same as a D chord, but moved up however many...for example:-

-4--
-5--
-4--
-2--

would be an E chord, (The shape is the same, except it's been moved up a tone).

I'm sorry I'm not examplaining this too well, I'm in a bit of a rush...e-mail or post a reply if you still need help and I'll go in to better detail....

willdridge@hotmail.com (original, huh?)