That response is referring specifically to the physical ram in the pc.
That being said a gpu can also alleviate system memory usage by using it's own memory.
http://support.dell.com/support/edocs/systems/opgx270/en/ug/specs.htm
Chances are your pc only has 1GB most likely 512mb of ram.
You can check by entering System Information in the control panel.
If you're running XP and only have 512mb adding another 512 mb ram module= 1GB should be fine.
Btw i bought a used GX270 for my mom and it came with XP and only 512mb of ram.
Most games include the minimum and recommended system requirements on the box or somewhere in the documentation.
This site is very handy for determining if a pc will run a game or not.
http://www.systemrequirementslab.com/cyri/