Your computer specs seem fine - you're obviously not going to be able to run high detail at full HD resolution, but at 1280*1024 I would have expected it to be OK at low detail.
I think your graphics card is the weakest link - it might be worth turning off hardware PhysX in order to free up more power for 3D graphics. If you right-click on your Windows desktop and select "NVIDIA control panel", you should have an option for "Set multi-GPU and PhysX configuration" under "3D Settings". From here, under "PhysX Settings" set "Processor:" to "CPU" and click "Apply".
IF that doesn't make any difference, then you'll probably have to play around with the advanced graphics settings. You might even have to drop resolusion to 1024*768 - but if you've got an LCD monitor with 1280*1024 native resolution I can understand how this would be annoying.
Good luck - the game is definitely worth the effort
