When running the game, the game starts with the Codemasters startup video. But it is lagging a lot. The same with the missions when clicking the story missions (haven't tried the others yet though). I once played a game with the same problem, and i was told to change a number from 1 to 0 in a gamefile, which solved the problem entirely. Can i do something like this for Worms 4 or do i have to get a better gfx-card or something?

hmm...
Go into C:\...\Worms 4 Mayhem\data\FMV\english\ and play the meet_the_professor vid. Does that lag too?

Nope, not at all, and i've run several videos on my PC without any problems at all. But it is something that often happens in my games. Caesar 4 is another example. Have you never heard this happen before in Worms 4?

Make sure the resolution of the game isnt so high that the video would lag.

The only thing that worked for me, was turning of the videos in the game and watching them outside, the way Plasma mentioned.

Hum, too bad. But ok, will do it that way then. Resolution change doesn't work for me - and i don't think the videos change resolution, only the game itself.