Why doesn't Compiz work on an Ati card?

[Chanchao]

I have an Ati Radeon card in my desktop comptuter. 9200SE I believe.

I try to enable Desktop effects but it doesn't work.  I also checked the
Restricted Drivers Manager but it says my card doesn't need them. (Is
that true?)

Strangely enough, I also have a VERY basic low end laptop with Intel
graphics, and all the bling works like a charm on it, never had to do
much to get it to run. Just added the Compiz manager (GL Desktop) to
have a sane way of configuring the options and that was it.

So should it work on an ATI card?  SHould I just go with Nvidia?

Cheers,
Chanchao