Signal transfer from PC to TV

I had it set-up and working with my old monitor, but when I got a new HD monitor, my videocard (nVidia Geforce 6600) is convinced my TV is also HD. I’ve tried to set-up the signal transfer from scratch again, but the only options are for HD TVs. The lowest resolution I can get for the TV output is 1024*768.

How can I have HD output for my PC monitor, and Low Def output for my TV set?