NO NEED OF DOING THE ABOVE COMPLEXITY!!!!
here is a simple way to do!
1)Note that if you are using Windows Vista as one of the operating systems, you will need to make this change from Vista, not XP.
2)First, you'll need to right click on Computer and select Properties:
3)Next, click Advanced System Settings
4)Now click on the Settings button under Startup and Recovery
5)And just select the operating system you want to use
You could also use the "bcdedit command" to do the same thing from the command line, but it's probably easier this way.