well the tv also undoubtedly has an hdmi port. this is your best bet, because it is capable of sending both video and audio from your computer to the plasma tv. now this is only gonna work if you have a pretty new ati graphics card. either the 2000 or 3000 generation. you can hook a hdmi cable and watch it on big tv. if you don't have an ati graphic card, then you won't be able to get the audio just through one cable. you will have to use an additional cable and the vga cable. vga would be the simples and cheapest way to get video from the computer to vga in plasma. your computer undoubledly has a vga port, so all you need a vga cable long enough to reach the tv. if on the back of your comp you have a s-video, you can use that.
to help you out more, it would be helpful to know what kind of graphics card you have, this would show your limitions. Also listing your computer specs would be helpful.