The ALSA-sound works out of the box if you activate it in the kernel. You should add a

ALSA_CARDS="snd-intel8x0"

in your /etc/make.conf before emerging the alsa things.

To be able to have multiple applications playing sounds, I changed the ~/.asoundrc:

#/home/cweiske/.asoundrc
pcm.ossmix {
        type dmix
        ipc_key 1021
        slave {
                pcm "hw:0,0"
                period_time 0
                period_size 1024
                buffer_size 8192
                rate 48000
        }

        bindings {
                0 0
                1 1
        }
}

pcm.!default {
        type plug
        slave.pcm "ossmix"
}

pcm.dsp0 {
        type plug
        slave.pcm "ossmix"
}

ctl.mixer0 {
        type hw
        card 0
}