Media Accelerator Games Jumpy.

I have installed a new game but it is jumpy. It isnt jumpy all the time. As
its a car game and other cars and traffic go by its then when it goes jumpy
like it has a shortage or graphics memory or something. Is there a booster i
can add to my Media Accelerator or anything thaat will increase the memery.

I am running Windows Vista Home Premium
2GB Ram
and 1.4Ghz processor.

The game is 18 Wheels Of Steel Convoy but it was made in 2005, and even when
i change the graphics to low there is no change.

Thanks in advance