If you have an ATI video card in your netbook, right click on the desktop, click ATI Catalyst Controller, and under Display Properties, select your HDTV setup, you can stretch, center, or scale to fit.
If you are using Nvidia gpu based netbook, right click, and select Nvidia control panel, go to set up display/screen resolution, select your display output, and change the resolution or stretch or scale to fit.
If you are using Intel GMA, then right click on the desktop, and select Intel Display Properties/Settings, go to HDTV setup, and select the suitable options
*note* these are basic troubleshooting options, for specific device assistance, the netbook model number and brand would help.