If you want to be able to choose which OS to boot into then:
1) Open System by clicking the Start button , clicking Control Panel, clicking System and Maintenance, and then clicking System.
2) Click Advanced System Settings. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
3) Click the Advanced tab, and then, under Startup and Recovery, click Settings.
4) Under System startup, in the Default operating system list, click the operating system that you want to use when you turn on or restart your computer.
NOTE: If you only see one operating system then a good tool I use is EasyBCD (Here is the free version - the download link may be confusing to find.. it is the big link that says DOWNLOAD with an arrow next to it with the text "OR ADD TO DOWNLOAD BASKET) :
http://www.softpedia.com/get/System/OS-Enhancements/EasyBCD.shtml
You can rename each entry so you can tell which one is which.
Best of luck