How are your FPS now? You may need to either update the drivers on the graphics card, or just upgrade the card and that can get you somewhat better performance, depending on the rest of your system. Installing more RAM can also increase your performance, unless you have 3 GB or more, then you probably won't notice the performance gain in a RAM upgrade.
I know when I got my new Gateway LX6200-01, I was running the integrated ATI HD 3200 graphics and got less than 30 FPS on most routes. Now I have an ATI Radeon HD 4850, and the only thing holding me back now is the AMD Phenom 9500 processor, but soon to be AMD Phenom II 940 processor. I also have 8 GB of RAM, so the only bottleneck in my computer is the processor.
Running 2006, I can get on average about 20-30 FPS on a route like Marias Pass, 30-50 on Death Valley Line, and less than 30 on the Darjeeling Himilayan Railway just to give you a comparison. Also, I run with the settings all maxed out (24x Anti-Aliasing, 16x Anisotropic Filtering, High quality Mipmap detail, Quality Adaptive Anti-Aliasing, and maxed in Trainz)