Apple has removed the FTP management functions in Leopard’s System Preferences. However it is still possible to run FTP on your Mac under 10.5.

To start the FTP service in the Terminal type:
sudo /sbin/service ftp start

To stop it type:
sudo /sbin/service ftp stop

Enjoy

Addendum:
Duh! It looks like Apple moved the “FTP” and “Windows” under Options in the Sharing Preference in System Preferences. Oops!