tjuh has problems with sound in linux, so i decided to write something here to act as a guide

he uses alsa on his internal soundcard. most internal soundcards don't support hardware-mixing; this means that only one application can grab the soundcard and output sound at a time.
solutions for this are:
1) get a proper soundcard. any soundblaster will do - you can grab them for €10 at ebay

2) use software-mixing.
2.1) alsas internal software-mixing. this is bullshit. don't use it.
2.2) pulseaudio. you have to configure some stuff and it is probably overkill for small setups, but it does the job (and a lot more).
3) get oss4. oss4 is the new release of the old (and abandoned by linux) open sound-system. it has studio-quality software-mixing and a lot of other nice features (control hardware-routing on the soundcard, etc). it doesn't support usb and bluetooth, though.