If you use a DVI or VGA converter...there is NO sound...you will need seperate cables for sound....HDMI does video AND sound...
All the best Brett
+1 forgot to mention this sorry.
You will still be able to get sound from your computer speakers no matter what connection you use, but unless you use HDMI you will be unable to play sound through your TV. For most users this wont matter since their computer speakers will have better sound quality anyway, however it's useful when watching a movie or something to be able to sit back with your TV remote as the volume control.
there are also converters available to convert DVI to VGA or HDMI. Though if you only have VGA/D-Sub I think you're stuck with going VGA to VGA which might limit the resolution you're able to have on the TV. I know my laptop doesn't like doing 1080p over VGA to my 37" LCD, I have to drop down to 1680x1050 but it still looks very nice.
You can buy these from most PC stores/online hardware retailers.
In all honesty, if you don't know what a video card is, your probably not up to the task of buying and installing one in your system and possibly needing up upgrade the power supply too.
So, lets forget the video card, what video outputs do you have on the back of your computer? VGA? DVI? HDMI?
I don't have a video card, what do you mean video card? Where can I buy one?
Do you know what your PC model is? If buy it a complete setup like Dell or HP, it should have a model name/number. Give us that information so we can determine what components & what ports you have in it.