Running any user program on low port numbers on *nix systems is generally tricky, as low port numbers are protected and only accessible as the root user.
In the past, jetty’s suggested solution has been to use iptables or ipchains to configure the operating system to forward traffic for port 80 (for example) to port 8080 (for example). Here’s the FAQ entry on how to do that here:
Recently, we decided to make this easier by adding a new feature which means you will be able to invoke jetty as the superuser, but after the ports have been opened the userid will change back to a non-privileged user, preserving the runtime safety of your system.
This little gem can be found currently in svn trunk and is slated for release in the 6.1.0. Look in $jetty.home/extras/setuid for the code and the README on how to build it. As the build requires native libs, there are some system-dependent configurations you have to provide, so there are a couple of steps you have to do manually for the build.
The README.txt file has full instructions, but I’ll reproduce it here to give you the general idea to start you off:
BuildRunning Jetty as non-root user on port 80