probably low would run decently smooth, medium maybe also, but probably no anti aliasing or shaders/other effects
i think it will be fine, my brother has a pentium d @ 2.6ghz with a 9500 gt card? i think?
and it runs cod 4 very well and your pc isn't that far behind his is it? doesn't seem like it would be much a problem.
the game has a auto-detect button for settings anyways so you can play around with that