After installing slackware 9.1 initially I had no sound, finally after getting the guts to compile my own kernel ( ) I managed to get a fast booting machine that has working sound I have a problem though, I can't change the sound volume! i've tried aumix, kmix etc. but they make no difference to the volume! Any ideas would be greatly appreciated!

My soundcard is a SiS7012 if it makes any difference

ps. I'm still looking for help on how to back up my kernel (as in what files do I need to put onto a cd if I want to be able to move my kernel onto this machine again after/during a re-install)!

You need to adjust the PCM also. trying running alsamixer in a terminal or from the console. Press 'M' to unmute PCM and others etc. To save your settings after you adjust them with alsamixer type "alsactl store" as root in a terminal. Hope this helps. Just the first thing that comes to mind.

I tried running alsamixer but it gave me an error something like snd_card error - no such mixer device

I've managed to turn down the volume using arts (I've always had sound but it was at maximum volume!), how do I configure things so I can use alsamixer (and kmix etc)?

I am not on my linux box but I am pretty sure you can adjust the pcm through the other mixers. Not sure. But to configure your soundcard type alsaconf in a terminal and configure your soundcard from there... that should work.
Good Luck.