The Xfce4 desktop I have just tried on Linux Mint 14 is the best desktop environment to use if you are wanting to enjoy a dual monitor desktop. The panels can span across both monitors and the wallpaper can also be spanned across the dual screens. This means that it is a perfect desktop if you want the panels to span across dual desktops and a light and fast desktop with none of the bloat of the KDE and Gnome 3 desktops. Type sudo apt-get install xfce4 to install this desktop environment and then select it from the login manager to enjoy a nice Xfce4 desktop that loads in a flash and can be attractive as well. Upon the initial load of this desktop you will be asked how you wish to configure the panels. Just choose the default configuration and then right-click on each panel and select span desktops to setup the Xfce4 desktop as I have in the screenshot. I am finally happy with my Linux Mint 14 installation; the dual monitor setup is fun to use and having so much desktop real estate is a great help when watching a bit of television and doing work in a web browser at the same time. The Tint2 and Openbox combination is also another great way of setting up a dual screen desktop that is both fast and usable.
Sure the KDE desktop is very good; it can look just like Windows 7. But I wanted a desktop that works perfectly with dual monitors and would still be attractive. Since the Gnome 3 desktop interface is all about the tablet touch screen paradigm now; switching to Xfce4 makes a lot of sense. If you are using Ubuntu 12.10. Type sudo apt-get install xubuntu-desktop to install Xfce4. The main strength of desktop Linux is the sheer number of various desktops that you may install to customise your desktop. You can use the Metacity window manager with KDE; or use the xfwm4 window manager in Gnome 2.32.2 or MATE instead of Metacity.
There is a nice WIKI entry here that explains how to setup the Compiz window manager with various desktop environments: https://wiki.archlinux.org/index.php/Compiz.
How to make KDE look like Windows 7: http://www.securitronlinux.com/linux-mint-2/windows-7-lookalike-kde-themes-how-to-make-linux-look-like-vista-or-windows-7/.