Windows allows you to extend the desktop across both monitors, simply drag the mouse off the (selected) edge of the primary display to make the pointer appear in the secondary and vice versa - you can grag application windows across displays.
Note that alot of windows components will remember where they last were (Internet Explorer, notepad, media player, remote desktop connection). Close the application in the second display and they will appear there the next time you open them, some applications however do not - PowerDVD being my particular favourite for forgetting...