Getting a preview like in window 7 is not a big deal now in Ubuntu user. Avant window navigator create a wonderful preview with the number of the exact type of currently open document. Avant Window Navigator is a dock window navigator where you can manage your preferences, add different themes, applets, launcher etc. So if you Install Avant window navigator and try to find the window preview option you won’t get it. You need to do some tweaks. Of course you need Avant window navigator for this purpose. You can download that from Ubuntu software centre or use the follow command to install via terminal
$ sudo apt-get install avant-window-navigator
After downloading and install avant window navigator from Application>>Accessories>>Avant Window Navigator.
Now you need to download the DocBarX theme for Avant Window Navigator. To download it go to the terminal(ctr+Alt+T) and run the following command
sudo add-apt-repository ppa:dockbar-main/ppa sudo apt-get update sudo apt-get install dockbarx dockbarx-themes-extra
Now install the DocbarX applet for window Navigator
sudo apt-get install avant-window-navigator awn-applet-dockbarx
Now you need to install CompizConfig Settings Manager. If you install that from ubuntu software center. You can run CompizConfig Setting Manager from System>> Preferences>>CompizConfig Setting Manager After install it enable the window preview from Extra>> Windows previews
After you setup your window preview. Now you can simply start your Avant Window Navigator and add DocBarX.
If you want to change the DockbarX preferences you can simply access it from Application>>> Accessories>>DockBarX preferences.
If you are running the lower version than 10.10 then you need to update zeitgeist to a newer version. To update it run the following command on terminal.
sudo add-apt-repository ppa:zeitgeist/ppa sudo apt-get update sudo apt-get install libgtk2.0-0 libx11-6 libxcomposite1 zeitgeist
ScreenShot of Avant Window Navigator with preview in Ubuntu 10.10