So far it's seems that both will be shown behind closed doors on CeBit. The official launch of ATI's part in April, with availability in May.
Would've thought that Nvidia's part would be allmost here allready, but it seems to have gotten delayed.
Maybe they'll announce the cards at GDC (GameDevConferance), but not sure.
It would seem that Nvidia's part will be more advanced that ATI's (supporting PS/VS3.0), but unsure about speed. It will be one hot (in temperature) card if the rumour is correct (~150W).
ATI is willing to sacrifice margins to make sure they have the top-end card, and Nvidia needs the top-end card so we'll probably see some nice prices for us.
Was this some of what you were looking for?