I think what psionics is looking for is Virtual Desktops.
A virtual desktop may also refer to setting up separate desktops for different groups of applications and being able to switch back and forth with a hotkey. For example, an architect might have one desktop for CAD and related design programs and another for spreadsheets, word processing and business applications. Grouping applications in this manner keeps the desktop from having an excessive amount of open programs on screen or on the Taskbar at one time.
Microsoft has one that is part of Microsoft PowerToys for Windows XP which can be found here;
A quick google found this opensource project VirtuaWin - The Virtual Desktop Manager