In order to install N-Gage client on your Symbian s60 5th edition mobile you need to first follow the steps in my previous post on hacking the mobile. Then Continue:
Download RomPatcherPlus_3.1.sisx on your mobile.
Enable all patches and exit.
Download and install N-Gage client.
Download and install any N-Gage game – like Asphalt 3 N-Gage.
To play the game:
First launch Rompatcher and disable all patches(else game will not work)
Launch the game and play!
After playing exit the game and re-enable all the patches.