In the advanced section of your graphics card properties screen you should have a option tab for Device Selection - usually that tab will have radio buttons for selecting analogue monitor or TV. If they are not there try installing the latest detonator drivers. Hope this helps.
One more thing - the GEFORCE 3 only has 1 RAMDAC so you can't view TV & Monitor at the same time - If you want to use your PC through the monitor and watch a DVD on the TV at the same time you'd either need another video card with twin view capabilities or if it's just for DVD decodong a hardware decoder card with TV output. I had a creative DVD decoder card, but it was too old for XP...the win 2000 drivers were none too stable and unless I find some new drivers I won't give it a try. I'm considering going dual boot and putting win 98 se on, but I'm not sure if 98 will boot on a dually - it might freak out as it can't cope with 2 processors, but then again it might only recognise the first one and be OK...or I could just put the card in my other rig which is running ME with an old Athlon 600...should be up to DVD playing!!