some single player missions run very slow

[HANSVEBEL]

hi Nike it, i wanted to say that the game is gantastic, i am hving though some problems with certain missions in the single palyer. in blazing lands some missions like the last one is going very slow and i can play it with difficulty. also in other missions this also happens. i was wondering is it something you know and fix with a patch or is it my pc?
i have a pentium 4 (3.0), envidia 7600 gs (saphfire), ram 1,50 gb, plenty of space harddrive, windos xp ser. pack 2,
can you help?