5450 would run Source games like Left 4 Dead. At 1280x1024 resolution and medium graphics settings it could get 30-35fps most of the time.
COD4 would also run but I think you might need to use low graphics settings to get the same 30-35fps most of the time.
COD5 run @ 1280x1024 and max graphics quality reached about 15fps.
Left 4 Dead at max quality: