I'm not too familiar on EXACTLY how drivers and hardware relate to one another.

I want to know what it means when a 3d chip manufactuer (ie: ATI IMAGEON 2300) says they support OpenGL es. Does this mean that I can call OpenGL Es functions on what ever device carries the chip or does the device manufactuer have to implement an SDK that delegates the function calls to the 3d chip?

For instance: If a new Dell AXIM pocket pc ships with an ATI IMAGEON chip can I make calls to OpenGL Es or does Dell, have to include and OpenGL Es API?

Are there books and/or resources that discuss this type of lowlevel access.