I don't think you need any special software to do that do you?
While you don't need any special software to use two monitors, there are certain things that you can get from multiple monitor software which you don't without it that are 'very-nice-to-haves':
With ultramon you get the task bar working so that the windows that appear on monitor 1 are on the monitor 1 task bar and the windows on monitor 2 are on the monitor 2 task bar, etc.
You can easily switch apps between monitors without having to un-maximize them, moving them and re-maximizing them.
You also can put different screen savers on the different monitors.
Ultramon costs about $40 but has significantly enhanced the multiple monitor experience for me. There may be other similar programs that are cheaper or free; I'd recommend finding one as I found the unmodified Windows7 multiple monitor experience less than completely satisfactory.
Full disclosure: I don't have any financial connections to the company that makes ultramon.