Dammit... I replied to your other post but it got deleted
Anyway, try some different older drivers... if that doesnt change anything its probably a bad vertex pipeline on the card. Itl most likely need replaced.
If you have any choice, get a different card too. A 512Mb 6200 is like a scooter with racing tires... the memory does nothing because the card is just too slow to take advantage of it. A 256Mb 6600 or even a 128Mb 6600GT would give you far far better performance.