I want a better graphics card for my computer need help?

my computer is old (2002) it is a hp microtower 7200 desktop. it runs ddr2 ram. and came with a graphics card that is not good enough. i want to be able to run games like rift with decent graphics i think i need PCI graphics card tho i have no clue where to look and what will fit my computer for certain so that i can buy it.. please help me!