[Fyron]

rstaats10 said:
"There are programs that allow for use of multiple operating systems on the same pc. You can switch between operating systems instantly with a click of a mouse and share files."

Sounds like an emulator, probably Virtual PC or VMware. Note that this works fine for regular programs, but is very problematic for gaming; until very recently, no emulator actually had any sort of emulated 3d video card. VMWare now has one, but it is still very primitive.

Atrocities said:
"I had considered the option of adding a second HD to the system but wasn't sure how to go about using it as a bootable drive for VISTA. I would like to be able to select between the OS I run."

With any recent NT based OS, you simply select the drive you wish to install to (can be literally any drive), and it will set up the boot loader with any detected installations of MS OSes automatically. You will then get an extra loading screen when you power on the PC, with a list of available OSes (and a 30 second timeout by default). The last OS you install will be the default choice, but you can edit this however you like with the MSConfig.exe app.