If you are using Windows XP then all you have to do is edit the boot.ini file and remove the unwanted boot entry.
When you open boot.ini it will look something like this:
Code:
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Windows XP Professional" /fastdetect
multi(0)disk(0)rdisk(0)partition(2)\WINNT="Windows XP Home" /fastdetect
Just remove the unwanted entry
Or if you are uncomfortable editing the boot.ini file or if you have Vista then use a 3rd party tool like
VistaBootPro, even though the name is VistaBootPro it works fine on both Windows XP and Windows 7.