LSD-graphics? WTH?

[psychodation]

hi everyone,

I just converted a freind of mine to the wonderful world of CIV IV.
Bought the whole thingy for her, installed iit. started well... but after four or five minutes the game always starts to do inexplicable things like changing and blurring the graphics. mostly in LSDish kind of colours...
never before any of these problems on this computer. works well with graphic-heavy programs like x-press and stuff...
civ updated, drivers updated i think...
any idea what the source of these problems could be?

thanks,
p