The Ubuntu default desktop uses the Gnome window manager, but there are a number of different window managers that can be installed, including AfterStep, Enlightenment, KDE, Xfce, Blackbox and Fluxbox. Installing IceWM is a simple process. You will want to make sure that you have selected the alternate install repositories. Open a terminal window and use the following command:

sudo apt-get install icewm

Once the install is complete, log out and click on the Options button in the lower left hand corner: You will see a menu listing all of the window managers installed on your system. Select icewm from the menu, and continue to log in. The IceWM desktop is pretty simple, although you can theme it to look like whatever you want. There's even a Windows XP theme that you can download. This is the default desktop:

The "start" menu is actually tied to the Windows key, as well as right-clicking on the desktop. Clicking the minimize and "restore" icons right next to it will minimize all windows, and show a list of windows, respectively. Pretty useful.