How to get XGL and Compiz working
Complete tutorials are to be found on ubuntuforums.org and I do not think it is necessary to repeat it here. But only for one simple remark.
The original tutorial on ubuntuforum.org makes compiz work without the opacity plugin. If you do it this way it will work.
First of all follow this howto: http://www.ubuntuforums.org/showthread.php?t=131267 and play around with it.
If you then download the packages from this page http://www.ubuntuforums.org/showthread.php?t=139265 and install the packages using dpkg -i.
After this all is well.... ;) See my screenshot http://www.ubuntux.org/my-desktop-running-xgl