ATI hasn't launched the R600 yet and it is already planning its next launch of a die shrinked version. It won't be launching the 1024 MB graphics card until Q3. It plans to launch the R650 chip and brand it as Radeon HD 2950XTX, 1024 MB GDDR4.
The chip is called R650 and it is a 65 nanometre core, how convenient. With this new chip ATI might have a fighting chance against the Geforce 8800 Ultra, but the real question is what will Nvidia have at that time.
The cards are scheduled for late Q3, so you should expect them to arrive in August or September, unless they get postponed.