very common mistakes by noobs...confusing system memory and graphics memory and vice versa.
graphics memory has nothing to do with system memory...
a graphics card is a separate system of its own...
in purchasing a new graphics card, look at the following basics;
a. graphics card interface on the motherboard either a PCI-E 2.0/1.0 or an AGP.
b. your current power supply and graphics card power requirements
c. graphics card cooling
d. price