[Jerom]

Looks like you're having the same problem my friend had when he tried to play Graal with his voodoo video card =\
Cept on his computer, they looked more like dots on the screen, although very similar to your problem.
During the day when there isn't any seteffects being used, it wont lag.
The only thing I can suggest is updating your directX, and if you're using a voodoo, get a normal video card.