EDIT: This seems to work on my CentOS machine but not my Ubuntu box.
$ which gem
/usr/bin/gem
$ which padrino
/usr/bin/padrino
$ which padrino-gen
/usr/bin/padrino-gen
sudo gem install padrino
$ padrino g project demo-app
padrino: command not found
bundle exec
padrino
this worked for me in Ubuntu 11.04
# Setup Ubuntu LTS 10.4
sudo apt-get install ruby
sudo apt-get install ruby-dev
sudo apt-get install sqlite
sudo apt-get install libsqlite3-dev
sudo apt-get install irb
sudo apt-get install rdoc
sudo apt-get install libopenssl-ruby
sudo apt-get install g++
wget http://rubyforge.org/frs/download.php/69365/rubygems-1.3.6.tgz
>tar zxvf rubygems-1.3.6.tgz
cd rubygems-1.3.6
sudo ruby setup.rb
sudo gem1.8 install rake rspec padrino --no-ri --no-rdoc
padrino g project foo -d activerecord -b
padrino g admin
padrino rake ar:setup