Can You Upgrade Graphics Cards on New iMac dc’s?

Ive got one of the new dual core imac’s the basic one with 128mb vram graphics card. Can you upgrade these cards with the ones in the higher spec imacs or third party cards, if so what sort of price are they and are they easy to fit?

I have not open one of them but as far as I know the Video card is going to be integrated into the logic board. This means you cannot upgrade the card without purchasing another logic board ($$$).

Sorry for the bad news.

cheers anyway!