Apple has removed FTP-server from System Preferences, but it still exists in the system. To enable it in your MacOS X Lion, just type in terminal:
sudo -s launchctl load -w /System/Library/LaunchDaemons/ftp.plist
Then you should start it:
sudo launchctl start com.apple.ftpd
To stop the server, just type:
sudo launchctl stop com.apple.ftpd
Also it’s possible to disable FTP-server again:
sudo launchctl unload -w /System/Library/LaunchDaemons/ftp.plist