The easiest way to do this is to right click on 'My Computer', go to 'Properties', then 'Advanced', 'Startup and Recovery'. Uncheck the box that says 'Time to display list of operating systems' and set the full install as default.
There is also a hidden file (C:\boot.ini) that contains the settings for bootup. You can remove the partial install from this. Make sure you delete the right one though
