is the 9600 gt a good graphics card for playing games like Sims 3 and Skyrim at high/really high graphics settings while having lots of graphical mods? I am a heavy gamer and I like to play games at top quality.
No you need a much more powerful card for that.
To play modern games at max setting you need atleast a HD 7870 to get 40+ fps for higher fps you need HD 7970 ot GTX 670
The gpu I suggested also consumes less power and has low temperatures.