This is one of the most commonly asked question and lot of people struggle with this.
If you are also facing this issue, follow the following steps:
For Windows XP & Vista:
1. Click on Start and then click on Control panel
2. Double Click on the Printers option
3. Right Click on the installed printer or the one that you intend to use
4. On the pop up menu, left click on Properties
5. On the small window, you will be on the "General" tab. On this tab, click on the "Printing Preferences" button
6. On the next window, click on the "Finishing" tab
7. Under the Document Options, click on the check box "Print on Both Sides (Manualy)" to enable it
8. Select the appropriate "Booklet Layout". If you don't need a specific one, let the option stay at "OFF"
9. Click on "Apply" button and then click on "Ok"
10. Click on "Ok" on the next window
You are set to print the document now. Happy Printing.