I had exactly the same problem after upgrading from 2.6.2 to 2.6.3. The computer tries to load X, video attempts to initialize 4-5 times, then the screen goes completely blank - can't even get console. It's not frozen, though; I can still tell it to reboot.
Standard XFree 4.2 drivers ("nv") work, and the nvidia drivers still work with 2.4.25, which I'm using at the moment.
GF2MX-200 video, Asus A7N8X-X motherboard, running Debian Sarge, latest official video drivers, fast writes enabled.