Thank you. :)
Well, The motherboard is an AsRock K7VM4 (
http://www.asrock.com/mb/overview.asp?Model=K7VM4 )
I'm using WIndows XP Sp3, and everything worked fine with my previous card, thanks for your quick reply.
EDIT:
I looked up a bit about artifacts, and it apparently it can just be a bad chip?
Or could there be something else which has caused the problem?