The "Ask Dave Taylor" website has three ways to accomplish what you want, and
the first one does not even involve tinkering with the master boot file.
"Click Start, right click on My Computer, and click Properties.
Click the Advanced tab.
Under 'Startup and Recovery', click Settings.
Here, in the 'Default operating system' drop down box, you will see two
choices. You can manually edit your boot.ini, the file containing the list of
operating systems that can be booted, but I would not recommend this unless
you're familiar with boot.ini's cryptic format.
If you get it wrong, your system isn't going to boot anymore and it can be
ugly to get fixed. The easy, trouble-free way to get rid of this menu is to
just uncheck the 'Time to display list of operating systems' box, and make
sure [the version of Windows you want to use] is selected in the drop down box.
Click OK, and click OK again. Then restart your system, and you'll see the boot
menu is gone."
You can always read the page referenced above if you want to use another one
of the methods.
If you need any clarification, please feel free to ask.
Google search on: "Windows XP" version select boot
Looking Forward, denco-ga - Google Answers Researcher