Here is the CORRECT way to install the Aurora GTK engine if you need it for themes. If you’re on Ubuntu 9.10, add this to your /etc/apt/sources.list, then run apt-get update. You’ll now be able to apt-get install gtk2-engines-aurora:

deb http://ppa.launchpad.net/merlwiz79/aurora/ubuntu karmic main
deb-src http://ppa.launchpad.net/merlwiz79/aurora/ubuntu karmic main