When you boot the XP and get to this DOS screen to ask to select which operating system to start with. How do you change and let the machine boot itself.
Go to Start > Open Control Panel > Performance & Maintenance > System.
The screen above will prompt up and choose the advanced tab and click Settings in the Startup and Recovery section.
On the Startup and Recovery screen, select Microsoft Windows XP Professional (or Home depending on your version) as your Default operating system and uncheck the box next to Time to display list of operating systems. The next time you reboot, your computer will automatically load XP.