Depends on which FTP server is/was installed. Check with:
rpm -qa | grep ftp
And post up what you get. Be sure the FTP server is running:
Where FTPSERVER is the name of the server installed (which should be revealed from my above command).
1. Depends on what server.
2. useradd or userdrake, or fire up an X session and use a graphical tool.
3. Too many possibilities, but check to see the server is running first.
And, as a side note, how do you know it's not because of Firewall, Mandrake comes with a built in Firewall...