Have you checked your permissions for /dev/dsp and /dev/mixer? Make sure those other than root can use them. In terminal as root type:
ls -l /dev/dsp
ls -l /dev/mixer
If they don't look like this:
crwxr-xr-x
then you need to do as root:
chmod 755 /dev/dsp
chmod 755 /dev/mixer
This will give you the proper permissions to get sound. Log back into X and check the volume levels of your multimedia player. This should get you in business. If it doesn't work, let us know and we'll see if your soundcard is properly installed. Hope this helps.