Currently Nautilus is the default file browser in Ubuntu and Nautilus Elementary is a patched version of Nautilus with an emphasis for simplicity.
Install Nautilus-Elementary in ubuntu 10.04 (Lucid)/9.10 (Karmic)
Open the terminal and run the following commands
sudo add-apt-repository ppa:am-monkeyd/nautilus-elementary-ppa
sudo apt-get update
sudo apt-get upgrade
After completing installation you need to restart nautilus
Nautilus Elementary Video