First you need to add the Pithos repo to your source list. Enter terminal with ALT-F1 and enter the following commands.
Edit your ubuntu source list.
sudo nano /etc/apt/sources.list.d/ubuntu.list
Paste the following to the end of the file.
deb http://ppa.launchpad.net/kevin-mehall/pithos-daily/ubuntu lucid main
deb-src http://ppa.launchpad.net/kevin-mehall/pithos-daily/ubuntu lucid main Now update apt with
sudo apt-get updateInstall Pithos
sudo apt-get install pithosNow simply navigate to the dashboard, page 2, local apps and "add a local app". Select Pithos and you're good to go!