For example, my computer has "Hard Drive 1". Then I take it out, and use a new "Hard Drive 2". HD2 has nothing on it, and I reinstall windows and all the drivers for the laptop on it. HD2 is functional and I use it. Later can I just swap out HD2 with HD1 and expect HD1 to work?
Yes, but any work or data saved on HDD2 will not be on HD1 (probably stating the obvious ). As long as you don't format or do anything else with HD1 while HD2 is being used, you can safely go back to HD1 and use it the way you left it.
What you're describing is what's used in my lab often; one HDD for a test platform, and another HDD for a second (xp vs 7).