well, at first i thought the word "commandline.txt" is very famous for majority of GTAIV player. nevermind, so as i said, u can go to the nvidia control panel., check the 3D settings, make sure:
-multi gpu acceleration = single display performance mode
-texturing quality = high performance
im not sure if it works or not, but it works in my system. of course, sacrifice quality for performance.
you can also try downloading "unofficial" driver for your geforce 9500gt.
another thing: you can lower your shadow quality and density so it give u more fps in night time. also view distance hogging your 9500GT.
lower these things down, you get more fps... even though it looks uglier, u can play smoothly.