How to find out what Graphics Card is present in your system?

The quickest (non-graphical) way to this is to run lspci | grep VGA in a terminal.

If you want you can also install hardinfo on your system, and when you launch it (system benchmark and profiler in the system menu), you can find your graphics information easily.

See this image for an example.

Use

$ sudo lshw -C display
  *-display               
       description: VGA compatible controller
       product: G73 [GeForce 7600 GT]
       vendor: nVidia Corporation
       physical id: 0
       bus info: pci@0000:01:00.0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vga_controller bus_master cap_list rom
       configuration: driver=nvidia latency=0
       resources: irq:16 memory:fd000000-fdffffff memory:c0000000-cfffffff memory:fc000000-fcffffff ioport:8c00(size=128) memory:fe7e0000-fe7fffff