Using the standard VGA output to a plasma or LCD screen is usually OK for web stuff or photos, but if you want to eek out the best possible video quality, you have to use the HDMI output of the PC (if available) direct to an HDMI input on the TV.
Also enable the "1:1 pixel mapping" function on the TV if available and check the resolution of the PC is set to the maximum your TV or PC can use, in my case 1920 x 1080.
Note that using an HDMI cable means it does not usually carry the audio signal.
When it comes to audio, if it's a laptop, then the standard headphone socket very usually doubles up as a digital optical output.
You can see this if you examine the socket carefully and see a red light eminating from it when you introduce a headphone jack to it.
In this case, you will need a simple fibre optic cable to link it to your amp.
If your PC is a full size model, it will almost certainly have a digital out socket, albeit probably coaxial phono socket rather than an optical port connector.
Just send this signal to the coaxial digital input of your surround amp using a single solid phono to phono cable to enjoy multichannel audio.
Using a straight digital out from the PC and into your amp will almost always result in superior audio versus using the separate analogue mini-jack output sockets, as onboard DACs on average soundcards are often not that good and tend to suffer from electronic noise generated from the motherboard's various processors.
The DAC in your amp will certainly do a better job!
If your full size computer doesn't currently have a video card that supports HDMI or DVI, it's relatively simple and cheap to replace the video card with one that does.
The increase in picture quality from using digital over analogue VGA is well worth it.
My picture quality from the PC is razor sharp with rock solid stability and brilliant colour definition on a Sony 52W4500 set.
Good luck, I hope some of the above info is useful to you.