If you are running a dual-boot setup with more than one Windows operating system, It’s pretty easy to configure the default boot operating system with the GUI interface. Note that if you are using Windows 7 or Vista as one of the operating systems, you will need to make this change from 7/Vista, not XP.

First, you’ll need to right click on Computer and select Properties:

Next, click Advanced System Settings

Now click on the Settings button under Startup and Recovery

And just select the operating system you want to use:

Easy stuff. You could also use the bcdedit command to do the same thing from the command line, but it’s probably easier this way.