Hello,
            This is my first question in this forum. I would like to know the simple way to
connect my computer with HDTV, so that all the movies or programs can be seen on it.
I have a Sony Vaio Pentium 4 CPU computer with 2.54 GHz and 1 gig. RAM. The TV is
LG HDTV 42" screen. What kind of cables are needed for Audio and Video reception.
I have already connected HDMI cable to TV and Cable Box.
Is this setup possible wirelessly through a router?
Any suggestions or tips would be greatly appreciated.

Forget wirelessly for movies unless you have a n-router and even then its inefficient. Depending on your video card and its output connections this is very possible. Ideally your video card output would be HDMI directly connected to your HDTV HDMI input.

   I would think that if you have the HDMI cable hooked up from your computer to your TV, that the TV would be treated as a second monitor.  You can look in Control Panel - Display - Settings tab and use the settings there to set up the TV.