Actually that would be a powertoy to have multiple desktops NOT operating systems running at once
For example you would have:
Desktop 1. Word open with Photoshop for working
Desktop 2. Internet Explorer and MSN Messenger
Desktop 3. A game
Desktop 4. Notepad open to save links or whatever
You can also set a different background for each to help distinguish, and with a simple click you move from one desktop to another (so its typically just changing the programs on your taskbar for easy managment and organization)