Hi :)
OK first I can tell you your pc is low end.. (which you already know so I will not go on about that lol.)
First off with nearly all expansions I would be sticking to the lower settings.. higher settings will work your card too high.
Next when you set the ts3 profile in NVidia control panel, did you do the optional step in this link : (after step 6.)
http://modthesims.info/t/481768
This step will allow you to double check if the NVidia card is being used for the game.
Next I would do a complete reset of the game folder :
http://sims3.crinrict.com/en/2011/06/tutorial-resetting-the-game-to-factory-settings-without-reinstalling.html
