Have you tried Finder -> Go -> Connect to server -> vnc://imac.address
I am concerned about the fact that you mention "Airport-based network" and then in the same sentence "Netgear router".
That makes me think (as I assum cabeandsuz) that you have both a Netgear router *AND* an Apple Airport Extreme or Airport Express router runnin in your home.
If you do NOT have an Apple router, then ignore the following:
If you do have both Apple and Netgear routers, then you may have 2 active routers in your home, and the Bonjour auto discovery protocols will NOT travel between routers. So your MacBook on the Airport Extreme or Airport Express router would not be able to see the iMac on the Netgear router, and the reverse would be the case because you are crossing a router boundary.
Airport Extreme and Airport Express routers can be put into "Bridge" mode via Applications -> Utilities -> Airport Utility -> Internet -> Share an internet connection -> Bridge. (or something like that). That would turn off the routing fuctions in the Airport Extreme or Airport Express and turn it into just an ethernet to WiFi bridge extending the existing Netgear router's subnet, so everyone is on the same subnet, and Bonjour protocols can access all your home computers.
