I can run the game at all setting max and on all resolutions max on my graphics card is 1280x1024.I run my game on max setting at the highest resolution and i get a good FPS rating from 90-125 but yet even when theres no action going on and im just running in the map my FPS will drop from 125 down to 2-15 fps and then again in a second or 2 rises back to 125 also when the fps drops like this my cg/ms frame goes from 8.0 to 300 or more ! even when i first load the map my fps is 3-4 fps then it rises back up after a while.
Probably because of only having 1GB of RAM; you're probably running out of space, and Windows needs to find room to put the new data. This is made worse by having a weak Core 2 CPU, which slows this process even farther.
More RAM should help.
1.86Ghz = Fail
1GB RAM = Fail
9800GT = Fail if you plan on maxing out all settings
lower your video settings if you want smoother gameplay....