First the game was not playable, froze every second.
after many hours of tweaking I used this:
+cvaradd jobs_numThreads -1 +com_skipIntroVideo 1 +vt_maxPPF 8

and http://www.gamesas.com/index.php?/topic/1239628-ati-hd-xxxx-and-dualcore-cpu-problem-solved/page__hl__cpu+dual+core
(with out the AI which didnt seem to help)

At first the game seemed to run smooth (but with out the best grafics) but after a short time the game starts to lag more and more each time I change an area or move to places in an area, I noticed its the time which takes the grafics to load.
so I think the problem is that the longer rage works for some reason the grafic card or cpu ran out of memory or go into some loop. I tried increasing the page file, didnt help at all.
btw I am using the latest patch for the driver amd 4870 series, so that might be the problem.
what do you think?