That indicates a problem with your overall strategy, because now the bootloader for both OSes is on one drive. If it fails, your other drive won't boot Windows. Do the second installation while the first drive is completely disconnected.
To resolve the problem you're having, right-click My Computer on the desktop or Start button, choose Properties, and then on the next panel, choose the Advanced tab, Startup & Recovery Settings button. Here you can disable the boot menu with the checkbox.
Also, since this is an Operating Systems topic and we are trying to get some momentum on proper categorization, I'm going to move the thread from Windows/PC Software over to Operating Systems.
AnandTech Moderator
mechBgon