Sorry, but more answers aren't going to make your hardware any more suitable (faster, stronger) to run GTA4. You are certainly welcome to try running the game. Even at the lowest settings, performance is likely to be poor.
It is old game yes but your hardware also very dated. Dual core should be the minimum for GTA 4 although i heard quad cores cpu fares bettercin that game. In fact it was among the first game that really shines on quad core cpu. Gpu side that 9400GT simply too weak. They were low end card when they come out back in 2008/2009 time frame. And GTA4 was quite demanding even for the fastest gpu available that time.
Sorry, but more answers aren't going to make your hardware any more suitable (faster, stronger) to run GTA4. You are certainly welcome to try running the game. Even at the lowest settings, performance is likely to be poor.