[AccessD] Duplicate code for nav buttons

My client wants the nav buttons on top of the form not the bottom, so I have
created them. I don't have the Access Developer's Handbook handy, and have
forgotten the slick way to deduce whether you're on the first or last row in
a given table. I can think of a couple of ways to deduce this but I would
love it if someone already has this code handy so I don't have to
experiment. I want to disable the First and Previous buttons if you're on
the first record, and disable the Next and Last buttons if you're already
there, and the Next and Last buttons to recognize that I may just have added
a row.

TIA,
Arthur