You have a very low end CPU and GPU in your system. That combo is typically only found in netbooks, and low end laptops. Your system was designed as a general purpose computer not a gaming computer. Like the guy before me said, you will have to try running the lowest settings that you can run. You may have to drop resolution in the game as well.
Where Hitman is a pretty demanding game, your lucky to even get it to run at all on your setup. Sorry to be the bearer of bad news.