Hi. OSS is deprecated in linux 2.6 onwards. You can still use it though.
What you need to do in order to use applications which rely on OSS, is simply install the ALSA wrapper for it.
For ubuntu i'm pretty sure you only need this package:
sudo apt-get install alsa-oss
You may have to log out and log back in for it to work.
Hope it works for you. If not, try rebooting afterwards.