sudo apt-get install pure-ftpd
echo "no" > /etc/pure-ftpd/conf/PAMAuthentication
sudo pure-pw useradd joe -u $uid -g $gid -d /path/to/web/files
#The $uid and $gid are the user/group ids for the user/group that owns the webfiles
sudo pure-pw mkdb
sudo ln -s /etc/pure-ftpd/conf/PureDB /etc/pure-ftpd/auth/PureDB