Virtual PC emulates a computer. You can create so called virtual machines and use them in a window in your Seven desktop. The screenshot here shows my desktop where a virtual Windows XP is running in its own session. I can install programs to that XP and run them exactly as it was a second computer with XP installed.
For example, I have Ubuntu Linux, Chrome OS, Windows XP and Vista installed on Virtual PC. I can run all simultaneously, at the same time, though it takes a lot of resources. Running one virtual machine at the time is no problem.
Welcome to the virtual computing!