It sounds like you need to get rid of your old videocard and buy a new one. You don't want to get into Crossfire technology (which is using 2 videocards at once) unless you're an enthusiast. And yes, those people are right, the memory (MB) on the videocard doesn't have a whole lot to do with its performance.
Run SIW and it will tell you all about your computer:
http://www.gtopala.com/download/siw-setup.exe