centrino does allow you to have a different graphics card.
Basis for a system allowed to be called a centrino is :-
Pentium M procesoor
Intel 855 chipset
Intel 2100 wireless card
For instance the dell 8600 is a centrino machine with a radeon 9600 Pro turbo option, not sure of the battery life, no doubt a quick google will find something.
But is a weight, battery, performance ratio, you can't have all three
