Ubuntu 11.10 freezes often. Driver problem?

I'm running Ubuntu 11.10 from a Live CD on a computer with Windows Vista installed. It has an NVidia graphics card. I don't want to alter this computer, so I don't want to install Linux.

After 5-15 minutes, it always freezes, although I think it happens when some graphics operation is about to happen. I suspect Flash ads might trigger it. (It actually didn't freeze when all I was doing was browsing Linux-help sites.)

When it freezes, the display stays the same, except that I can move the mouse around. Mouse clicks are ignored though (or at least no results are shown on the screen). If I was playing a video, the sound keeps playing.

About half the time, I can kill the X process by pressing Alt-SysReq-K, and it lets me log in again. 40% of the time, it does restart X, but the screen goes blank and stays blank. At this point, I reboot either with Alt-SysReq-B or hold down the power button.

The symptoms are consistent with what is described in:
https://wiki.ubuntu.com/X/Troubleshooting/Freeze

After restarting X, I looked at the result of running "dmesg", and spotted a line "fail pre-validate sync".

I am able to run Ubuntu 6 from an old CD I had, with no freezes. (Side point: It always changes the computer clock by a few hours! Was that a known bug?)

So, what's the solution?
a) Try Ubuntu 10 or a different flavour of Linux.
b) Get a new driver. (How? I'm a Linux newbie.)
c) Sorry, NVidia's driver for Linux is buggy, nothing you can do, use Windows.
d) ?

Also, what's the situation with Flash? It seems to be included with the Live CD, but only a few Youtube videos will play. When I went to Ubuntu's software centre, and searched for Flash, the user comments described it as very buggy. So what do people do?

Thanks in advance,