According to the Inq NVIDIA will ship some quantities of the NV40 Ultra and non Ultra in May, probably by the end of the month while the real batch will be available in early June.
The first beta Forceware 60 drivers were ready on the 15th of April. The release candidate driver is planned for the 28th of May. So probably the first cards will be shipped with a beta driver of the new Forceware drivers.
In June there might follow a price drop when the cards are available in quantity.
It ATI keeps its promise it will have quite few X800PROs at that time on the market and X800XT just ready to launch. And if ATI's claims are true Nvidia might have to play with releasing a higher clocked NV40 Ultra card. The NV40 Ultra 2 maybe?