Last night I installed the latest (non-beta) driver release from nVidia, having received a notice from their auto-update system that a new driver was available.
I installed it on an Asus laptop, with nVidia 240M GPU, Vista 32 bit.
On reboot, my screen went black and stayed that way.
Checking the internet (on another computer) I see that happened to a lot of people, including many platforms up to Win 7 64 bit.
A system restore from Safe Mode did not fix the problem. Still black screen.
But still in Safe Mode, I used the "roll back" driver feature in Device Manager to get back to my previous working driver release.
If anyone else experiences this problem, and wants more detailed instructions feel free to PM me.