Alt tab question for 12.04 LTS

[Linda]

This is mostly a just curious question.
   I have five machines now that have been migrated to 12.04 
LTS from 10.04 LTS.  They are using Gnome classic. 3 of the 
machines you can choose alt left mouse click to add 
launchers to the panel and Alt Tab to cycle through the open 
terminal windows. For two of them neither works.  Of course 
one of the machines where it doesn't work is used by someone 
who loves alt tab to move through windows so I wound up 
installing compiz so I could set it to use alt tab to switch 
applications. However I am mystified.  They all have 
basically the same packages installed and I ran through  all 
the gnome packages in synaptic and they seem to match.   I 
actually had uninstalled the compiz stuff off of all the 
machines because two older machines were freezing and it was 
one of the suggested causes.  Any idea of what program or 
configuration setting is allowing the alt tab to work on 
some of the computers? Also any idea how I can get the alt 
left mouse click to bring up the panel menu on the two 
machines where it doesn't work?
                   Thanks
                    Linda