As you've said that you've just installed slackware 10.1. I suspect that you did not run:
1. "alsaconf" to setup your sound card
2. "alsamixer" to set the default volumes
3. "alsactl store" to save the volume settings
Make sure that your "VOLUME" and "PCM" are enabled!!!
most applications would use NULL sound device, if they could not output sound to a hardware device.
also check out some stupid mistakes which even Super Computer users would do:
1. check jack connection at sound card is properly inserted to the "SPEAKER out" or "LINE OUT"
2. check power supply
3. check speaker volume (not alsa but physical device's knob)
4. are you ears closed ?