Your config will support the games you mentioned but @ 1024*768 with low to medium graphics setting.
graphics cards are compared based on directX/shader model version supports ( Like DX10 and shader model 4 ), architecture & series ( like ATI HD 4xxx series or Nvidia's 9xxx series ) and what kind of ram they uses ( ( GDDR3 or GDDR5 or DDR2 ) and their bandwidth and number of shaders in a particular series
graphics cards are compared based on directX/shader model version supports ( Like DX10 and shader model 4 ), architecture & series ( like ATI HD 4xxx series or Nvidia's 9xxx series ) and what kind of ram they uses ( ( GDDR3 or GDDR5 or DDR2 ) and their bandwidth and number of shaders in a particular series