If your old games, like UT, Quake2, or Rune, won't start or don't have sound due to the error "can't find /dev/dsp" on your modern Linux systems, it's because they were made when OSS (Open Sound System) was the preferred sound system in Linux. Alsa doesn't make the old /dev/dsp device so old games can't find the device to use.
If you run a Linux system like Mandriva or Ubuntu, that build their kernels to try and suite the masses, then OSS emulation is probably built as a module but maybe not loaded at boot. In that case all you really need to do as root is:
If you built your own kernel, you may need to make sure you have:
set: Device Drivers > Sound Card Support > Advanced Linux Sound Architecture > OSS PCM (digital audio) API to M