|If you have a modern motherboard you can isolate each operating system as long as each is on a separate hard drive. |
The advantage of this is that you can add or remove hard drives at will without messing up the boot files.
On the computer I am currently on the way to boot to any drive other than the default drive is to hit F11 at start up. You board should have something similar.
If you disconnect all but the drive you are installing to you will not have boot files on one drive that serve to boot another drive.
Another thing to note is that Windows 7 creates an extra partition that may be used for security of your system (see link below). If you don't need or want that feature then use a third party partitioning program instead of Windows 7.
One other point is this. When you have more than one identical hard drive installed in the same system and they are being used independently (no RAID), then when you are setting up the hard drive you can assign a label to each drive. This is imperative if you want to use the method I suggested above. For example, WinXP, Windows 7 x64bit, programs, etc.
If you don't do that, you will not know which drive to select from the menu. I have 5 hard drives and 2 optical drives installed. Each has a distinctive name.