You have two things happening here
First, the GT430 was a bad idea to upgrade to for gaming. It's not a very good value. You should replace it with a Radeon 5670, same price, 20%-40% better performance. http://www.guru3d.com/article/geforce-gt-430-review/8
Second, the Pentium D, although high in clock speed, is low in processing per clock. But getting a better video card should be the first thing.