Thanks for all your helps.
I went and bought a GeForce GT520. It was amazingly small compare to my old ATI all-in-wonder x1900 (1/2 the size). Anyhow; I installed the card, installed the lastest driver from Nvidia site. I plugged the HDMI to my receiver, VGA to the old monitor, DVI to HDMI to samsung plasma (DVI/HDMI port on TV as suggested). When I booted up the system, the VGA monitor was blank and my plasma tv got the boot up screen until the 4 colour dots of win7 startup disappeared then it lost the signal and back to the VGA monitor. I have tried to unplug all the connection to the graphic card except the connect to the plasma TV and restarted the system but the same thing happened. I went into the NVIDIA control panel and the only monitor that it can detect was the VGA. Under the NVIDIA control panel even I choose the "force television at startup" still didn't help. I updated the TV firmware to the latest, but still no luck. Any suggestion is greatly appreciated.
My system is win 7 64bit home premium