20" iMac G5 (2008) -> secondary display for 27" iMac (2011)?

Not via direct connect. That ability did not appear untl about 2009 in the 27-inch iMacs. Listing of qualifying models here:

http://support.apple.com/kb/HT3924

The only option is screen sharing:

http://www.screenrecycler.com/ScreenRecycler.html

NOTE: Can you clarify this?:

20" iMac G5 (2008)

iMac G5s were discontinued in March 2006. And by mid-2007 the Intel iMac had retied the old white case it shared with the late-model G5 iMacs. What does "About this Mac" say about the processor in the "20-inch" unit?