Complicated routing/SSH-FTP tunneling problem

[Daniela]

Hi all!

I have the following problem:

I'm running a FreeBSD SSH server.
Some clients can't connect to it. They are on a local network, connected to 
the internet through another server. This second server used to allow SSH 
login, and users could then connect to my server from the second server.

On the second server, SSH login isn't allowed any more. It won't route any 
requests to the outside, except for mail. The FTP port is open, however. I 
heard it is possible to create a tunnel over FTP, so the clients could still 
get to my server.

How could we do this (if it is possible)? Are there other ways?

Greetings,
Daniela