We've got a FTP server that's open to the public network and its running on Suse SUSE Linux Enterprise Server 11 (x86_64) SP2

Now, since it's an FTP server I can't disable that service, but how else do I harden this server from attacks from outside?

I am thinking of disabling the firewall and only allow communications with FTP ports, and also changing the Selinux to enforcing mode.

Anything else anyone can think of?