I am running Ubuntu 11.10 with Gnome Classic, and I got one more problem with the display.
When I launch programs, the corresponding icons are not on the bottom panel anymore...
How can I solve this ?
You will need to use one of the shown panel-applets.
Press Win+Alt and right-click the bottom panel bar - N.B. Win is the Windows Symbol key
(If you are using Gnome Classic (No Effects) i.e. gnome fallback mode then to add to the panel use Alt and right-click)
Lots more information and some very useful links to customise your classic desktop can be found in the linked question.