From their FAQ on the xmms.org homepage:
r9: My XMMS don't output any sound and it seems to go about 3 -> N times as fast.
Whoops, you have been using the diskwriter plugin, press ctrl + p and change the output plugin to either OSS or ESD. You might want to check the configuration for the diskwriter plugin, the path will contain a couple of well sized wavs.
http://www.xmms.org/faq.html#r9