|Right click on My Computer and select Properties, Advanced, Startup and Recovery's Settings button.|
Click on the Edit button and modify the file to have only a single OS to boot from.
Mine is a single boot with XP Pro and looks like:
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP Professional" /fastdetect /NoExecute=OptOut
Yours, if on partition(1) should show as partition(1) instead of (2) like mine.
And, change 'multi' to (0) like mine.
Point is to have it only show the single OS.
Before making any changes make sure to copy and paste it's original contents into a Notepad file and save it as boot.ini.txt for safe keeping.