A TV or monitor must receive two type of synchronization signals to recompose the picture. The Vsync is related to the refresh rate and because it's adjustable from the display properties, it can be made the same as regular TV-signals have. The problem is with the Hsync which has very different values for TV-sets and monitors: the TV-standard is around 15 kHz, while for monitors its typical values can be between 30 and 65 kHz. Probably your videocard's Hsync is around 45 kHz, that's why you see three times the computer screen. And you can't change that value from the display properties...
So to connect the TV-set to the computer you'd need a vga to composite (or S-Video) converter box, just like this one:
http://www.smarthome.com/7743.html