Sure it will RUN, but if you're actually looking for decent playability, I'm not sure your setup can handle it. GTA IV on PC has always been troublesome with even high-end computers, seeing as it's a (rather bad) port from the consoles. Try finding a demo and see how it performs.
I hv somewhat similar specs. The game will surely run however will not give good performance as the 9400 GT card is not a high speed card even though you hv 1 GB of it. So in the graphic settings, if you want the game to run smoothly, make sure that you are not using more than 400 MB of the VRAM ( DO not bother about the rest 600 MB ) or you will slow down your game. Keep Antiliasing off, reflections minimum, resolution not more than 1200