In the nVidia control panel, click on the TV menu and choose the output type (eg. PAL60 or NTSC). You may have to force it to use the TV if it doesent detect it automatically.
Make sure you choose a resolution low enough for the tv (i have to choose 1024x768 on my laptop's tv out in order to get a view of the whole screen).
Hopefully that should get you there, im sorry i cant help more, i dont have a nVidia card anymore.