Originally Posted by mr dave

Always check for a patch first.

You'll probably have to search the Blizzard site yourself since I only get linked to the US version but - Diablo II Patch Information - Support - Battle.net Support

I realize this is two weeks old but if you're still not killing all sorts of demons and stuff this other thread might help - Battle.net - English Forums -> Windows Vista/7 and Diablo II

And if that doesn't work... just get Titan Quest.