First you need to answer some basic questions: Do you have the latest drivers installed, and does Windows actually see both of your displays?
If the answer to both of these questions is yes, then do the following:
Right click on the desktop->Screen Resolution.
In this window you can choose how you want the displays set up; ie, cloned, side by side, etc. If they're side by side but they aren't in the right order, you can click on the little animated display and drag it to where it should be relative to your main display.
Hope this is somewhat helpful!