iMac (2009) as a secondary display for a MacBook Pro (new)

You are referring to Target Display mode. As you have a 2009 iMac, make sure you have got a Late 2009 27-inch iMac, which is the only 2009 iMac that supports Target Display mode. If you have got one, just buy a Mini DisplayPort cable, connect it to your iMac and the MacBook Pro, and press Command and F1 keys to use the iMac display as an external display. For more information about Target Display > http://support.apple.com/kb/HT3924?viewlocale=en_US&locale=en_US

[iCon] wrote:

If so, is it possible to do so wirelessly, ad hoc or wifi? (No is fine)

There's a way to use your iMac display as an external display without any cable, and it is compatible with all iMacs. You just need to use ScreenRecycler, that allows you to use your iMac as an external display for another Mac connected to the same network by Wi-Fi or Ethernet

You are welcome

I have used screen recycler in the past and it's very slow and jittery, Air Display seems to work A lot better

http://sites.fastspring.com/avatron/product/airdisplayformac