The Nintendo Wii, like any game console, requires a display in order for the games it plays to be seen. A special input made for the 27-inch iMac allows it to turn off its the computer electronics so it becomes, for all practical purposes, an LCD TV screen. A few specific-purpose cables from a computer store and a video game store will be needed to make this work.
Place the Nintendo Wii next to the iMac 27 inch desktop. Plug the console connector at one end of the HD Wii cable into the A/V output on the back of the Wii. Plug the red, green and blue cables at the other end of the HD Wii cable into the red, green and blue connections of the DVI-to-Component cable.
Plug the DVI connector of the DVI-to-Component cable into the DVI connection on the DVI-to-Mini-DisplayPort cable. Plug the Mini-DisplayPort end of the DVI-to-Mini-DisplayPort cable into the Mini-DisplayPort connection on the back of the iMac.
Turn on the iMac. The computer components of the iMac will remain inactive due to the plug in the Mini-DisplayPort connection. Turn on the Wii. Watch the Wii’s start-up screen appear on the iMac’s LCD screen.
You will need a pair of powered speakers to hear the audio from the Wii.
Don't force any of the connections together--this can break a connector.