Current OS emulators are capable of what you are asking. Here's quote from Virtual PC info:

"Virtual PC lets you create separate virtual machines on your Windows desktop, each of which virtualizes the hardware of a complete physical computer. Use virtual machines to run operating systems such as MS-DOS, Windows, and OS/2. You can run multiple operating systems at once on a single physical computer and switch between them as easily as switching applications—instantly, with a mouse click. Virtual PC is perfect for any scenario in which you need to support multiple operating systems, whether you use it for tech support, legacy application support, training, or just for consolidating physical computers."

So.. i guess you would also need both windows active same time. I'm not sure if that part is doable. Windows XP has only 1 active window at any time, and there the active window is 1 virtual OS even though many can be running.