I favor Mac, though in some situations I need to use a Windows machine. I really rely on the Spaces App in Mac OS X for sectioning off my different projects I am currently working on, email in one space, iTunes in another as well as any other random tasks I need to perform.
Dexpot on Windows works very similar to Mac OS X Spaces, though it is not a complete clone and some functions work a bit differently.
Overall, if you like using Spaces on the Mac, you should enjoy Dexpot.
You can download this free utility at http://www.dexpot.de