I know this is kind of old but, I just thought I would let all
know what I did to solve the problem with not being able to run Compiz
on my laptop (which uses an ATI Mobility Radeon 9200 graphics card)

It took a lot of time (seems like it anyway) going through the Ubuntu
Forums but, a similar problem had happened to someone before and, this
is what that user did to fix it.

Using the open source drivers supplied with Ubuntu, all I had to do was
create the following config file to my Home folder:

I typed the following line in a text editor: "SKIP_CHECKS=yes" (without
the quotation marks)
and saved it in my home folder as ~/.config/compiz/compiz-manager

I then tried turning on desktop effects again and WOW!!! I had wobbly
windows and everything! Almost everything in Compiz works without any
problems or apparent slowdowns to my older laptop here. As a matter of
fact, it feels brand new again!!!

Anyway, I just want to say that if your having problems with something
in Ubuntu, don't give up! Keep searching the forums (when you have the
time) and chances are, you'll eventually come up with either a solution
or a resounding "No, that ain't gonna work". Hell, you might even learn
something and figure out how to help somebody else!!