Is it possible to assign an extended desktop to be an external desktop for a window's machine?

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I have an iMac with Lion and a Windows Vists Laptop and corresponding external monitor on my desk. I'd ideally like to use my iMac as an external monitor for the Window's machine and essentially remove the physical one from my desk.  Make sense?
I already have 4 extended desktops created on my iMac and I'm HOPING that I could assign Desktop 4 (example) as the external monitor to be controlled by the Vista machine. I'd like to be able to flip between my Mac OS and the "extrernal monitor'' via the 2-finger-swipe gesture. Anyone have any ideas?
NOTE: I also have Paralles installed with Windows 7 running on my iMac, but I specifically need the Vista machine to have the external monitor, so please do not suggest this solution.
Thank you!  While reading these directions, I realized that I have the wrong connector.  I have the old Mac Monitor serial port to VGA instead of the MiniDisplay port to VGA needed (didn't even think about this computer not having that port available).  I just bought the correct one from Apple, so I'll attempt these instructions as soon as it arrives.
To confirm: I'll be able to run the iMac as the external display and have Lion open simultaneously, right? (Obviously not both on the screen simultaneously, but the ability to "switch" views) Based on the article, the trick is turning the Target Display on/off with the Command + F2 buttons (as opposed to assigning an extended desktop and using gestures), correct?
Again, thank you for your help!
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