First, download the Darwin Streaming Server binary for Linux (yes, it says it's for Fedora Core 4 and later, but it'll work for Ubuntu, too). My download was named DarwinStreamingSrvr5.5.5-Linux.tar.gz.
If you can read German, the following site should be very useful:
Or just do the following after you've extracted the files:
sudo addgroup --system qtss
sudo adduser --system --no-create-home --ingroup qtss qtss
To start the server:
You administer the streaming server through port 1220 in your web browser.