I run Slack 9.1, and all was well until I tried an unsuccessful upgrade of KDE from 3.1 to 3.2.3.
Now if I log in as root I can use /usr/bin/aplay to play a file, but as a user I get :
user@shetland:~$ aplay /home/user/test.wav
ALSA lib pcm_hw.c:1055:(snd_pcm_hw_open) open /dev/snd/pcmC0D0p failed: Permission denied
aplay: main:484: audio open error: Permission denied
user@shetland:~$
Have read about needing a group called "audio", I do not have one listed in /etc/group,
do I need one? (I assume that I never needed one before I broke it)
Trying to understand which files/directories I need to give "user" R/W/X permission for?
I have also run alsaconf after the "upgrade" to no apparent effect
all help appreciated.

OK, what I believe you are going to need to do is update permissions on the following files:

/dev/dsp*

/dev/snd*

/dev/mixer*

so, a command like the following might work well:

chmod a+wx /dev/dsp* /dev/snd* /dev/mixer*

Hope your sound problems are cleared up!

dont forget /dev/audio for some people