Assign a DNS name to Linux Server
 

How to assign a DNS name to a Linux Server
how to configure Linux Server enterprise 5 to activate ftp externally (outside LAN)

Purchase the domain with a domain supplier,
Point an A record for the domain at the server,
configure services that need to listen to that domain (ie add a reference for the domain httpd.conf for apache as approiate to the set-up you are after)


Linux Server Enterprise 5? do you mean Red Hat Enterprise Linux 5.x? Not sure what you mean else.

You will have to install an FTP Daemon,
Open up port 21 on the firewall (assuming a firewall is running as it should be)

Set-up FTP as necessary, remember that FTP is a very insecure protocol and that the SSH Daemon will already do SCP and SFTP already without the need of messing around with an FTP daemon.

These days I would leave FTP daemons to just anonymous downloads only...

If this is RHEL 5, here's the Deployment guide http://www.linuxtopia.org/online_boo...ion/index.html