The process is not quite as straightforward as it should be, but it works pretty well.

The secret lies in a nifty application called ScreenRecycler.  In a nutshell, it allows you to use a monitor connected to a second computer as an additional monitor to your main computer.  So yes, you DO need 2 computers.  The good news is that the second computer can be either Mac, Windows or Linux. The bad news is that it’s slightly slower if the second computer is not a Mac. My second box is running Windows and it’s very usable for e-mail and calendaring. 

My setup consists of:

• 1 Dell 24″ 2405FPW (awesome monitor btw)
• 1 Samsung 22″ 2243BWX (vertical)
• 1 Unibody Macbook
• 1 custom-built PC

Screen configuration:

• Main screen: Pretty much everything happens on this screen
• Vertical screen (left): Mail.app (top), iCal (bottom)
• Macbook screen: Twhirl, Corporate MSN Messenger, Adium

The -really- cool thing about my setup is that, if I ever need to use Windows, I can just stop ScreenRecycler and my Windows desktop appears on my left screen.  Because I use SynergyKM (and this), I simply have to move my mouse to the left and my keyboard and mouse automatically start controlling Windows. 

For your information, clicking the image will let you see my setup it its full glory!