Actually Nvidia didn't officially announce the new Geforce GTX 260 and 280, yet. But now there is a driver, which is said to have been intended for quality checks, available on the web.
There is an unofficial driver available for the GT200.
Several rumors indicate an introduction of the GT200 chip on June 16th. But a driver that has the serial number 177.26 and is dated to May 22th already got onto the internet. The driver package supports the Geforce GTX 260 and 280 exclusively. So if you want to use the new driver with your current graphics card, then you need to modify the "nv4_disp.inf" at first. The unofficial driver is available for Windows Vista and Windows XP.