Right click My Computer on the desktop and choose properties.
Then under the Advanced tab, choose settings in the startup and recovery section.
Then in there you can either reduce the time to 0, and or, if you're feeling brave, hit the edit button, and delete the bootup option you do not need.
Be careful... make sure you know exactly which line references the correct OS partition.
you can even try naming them first, to make sure you delete the correct one, just put a name in between the quotes,
example multi(0)disk(0)rdisk(0)partition(6)\WINDOWS="NAME HERE" /fastdetect