The problem is simple: i can't configure my 5.1 audio system.

So which driver are you using? ALSA or OSS? Does your sound work normally? What have you tried already?

On OSS driver,sound works ,but with bad quality and it has a noise when i turn up the volume. With ALSA it gives me an error message . it says "Please check if your sound card is configured properly or no other program uses the soundcard".I want to get these settings configured:
Output = Front Speakers
Line In = Rear Spreakers
Microphone in= Center Speaker/SubWoofer
My soundcard is Via 8233/ Ac'97

You can go two ways from here. Since you have a AC97 sound card you can't do hardware mixing. So if you want more programs to use sound at once you'll have to make the sound server work and run every program via it, or you have to edit some files to get alsasharing to work properly and turn off the sound server. There's a howto on it in called AlsaSharing in the alsa howto. I'm not sure if the sound server (knoppix is kde isn't it? The sound server is arts then) supports what you want but you might be better off trying to get it to work with Alsa itself and leave the sound server for what it is.

Unfortunately I haven't managed to get AlsaSharing set up properly myself so I can't help you much with that nor with the 5.1 sound but the ALSA documentation is pretty large so it might be in there. Also I'd check the Linux Documentation Project for info.

Hope this helps a bit.

this knoppix sux. Its quait buggy.it's just not met to be on HDD and i'm in some kind of experimental period so give me a suggestion of which linux distribution i should try next

Depends on what you want. If you like what it has from debian you can try debian. If you do use the sarge installer. But you might have to tinker a bit to get it all up. There are a few other debian based distros that will work installed on your HD. Might want to try those too or do something completely different but then you'll have to say what you want. Also just check distro's sites and try. Knoppix hard disk install will be unmaintanable in the end I hear as well.

I don't know which other things made you think knoppix is buggy but if it's your sound card you'll probably have that in more distros.