Logitech USB headset under linux

- compile the snd_usb_audio module (in devices -> audio -> usb)
- install the module: cd /usr/src/linux && make modules_install
- restart alsa: /etc/init.d/alsasound restart
- load the module: modproble snd_usb_audio
- make sure alsa has recognized the device: cat /proc/asoud/cards
- check sound levels (make sure it's not muted): alsamixer -c 1
- Test - play stuff with mplayer: mplayer -ao alsa:device=hw=1

Congratulations, you should be able to use your headphones now :)
Make sure you have the right number for alsamixer and mplayer (if your headset is your only device, the number would probably be 0)