Yesterday I finally got around to dual-booting my MacBook, with a nice fresh copy of Windows 7. Everything was great, except for a laggy download of the Windows Support Software. So, earlier today, I got around to installing the drivers. It turns out, my old MacBook didn't support BootCampx64. I then did a quick search on how to fix this issue. 

I came up with a number of answers, but this is an answer aimed at people who were in my situation which is:

• I could not right click on the BootCampx64.msi file, because of the missing drivers.
• Or if I could right click, then changing the properties of BootCampx64.msi resulted in not having the required elevated access privileges.

My solution (done from within Windows, obviously):

• Without the drivers installed, you can still right click on the BootCampx64.msi file by click it with 'Shift-F10' which apparently acts as an alternate right click.
• If you have the first step down, try opening the properties of the file, and change the compatibility to earlier versions of Windows.
• If that still doesn't work, then open the start menu. Then go to Programs » Accessories » CMD, and hover over CMD.
• Press Shift-F10, or right click if you are able, on CMD (the Windows Command Prompt).
• Select the option in the drop-down menu, 'Run as Administrator.'
• Then open CMD and get a shell window.
• Now, when you open CMD, you should be running it as C:Windowssystem32.
• At the Command Prompt, type in cd /d C:
• You should now have C: at the far left of the prompt.
• Type in cd Users. Then type in dir.
• Find your username, and then type in cd username, e.g. cd John Smith
• Continue the dir, cd process until you come into the directory in which the BootCampx64.msi is. (You may have dragged the WindowsSupport folder onto the desktop, or someplace else).
• After you have reached the directory, simply type in BootCampx64.msi.
• The program should start.
• All of the drivers should start installing. You probably won't be able to move your mouse if you have a trackpad, as I do, because the Apple Trackpad driver is one of the last to be installed.