Which drivers for ATI Mobility 9000

I have the onboard Mobility 9000 chip in my laptop and Vista does not install
specific drivers for it but detects it as a Standard VGA. I have found the
drivers for it in Vista and installed them, but find they test rather slow
when I run a diagnostic. Would it be better to install the WinXP drivers for
the chip? Or is that impossible or inadvisable due to the difference between
Vista and XP? Video drivers seem to be such a big problem that I wonder what
is being gained in Vista by changing the video system so much. I see no
improvement in the video display. Much grief would have been prevented by
just keeping the video system the same. I'd really like a good explanation
for the change...different doesn't always mean better.

Thanks to anyone with info on this.