Lestat may have hit the nail on the head there, but I hope for your sake that isn't the problem. Some other helpful info you could give us is:
1) What version of DirectX you are running.
and
2) What version of Baldur's Gate 2 it is.
Have you tried installing the latest patch and seeing if that helps? You can download the patch for BG2
here. You might also try turning 3D Acceleration on/off to see if that makes any difference.
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"Our deepest fear is not that we are inadequate.
Our deepest fear is that we are powerful beyond measure."