[PLUG] SSHing to a box behind a firewall... netcat maybe?

[Matt Alexander]

Computer A is running sshd and is behind a firewall that blocks all
connections initiated from the outside.  Computer B is on the outside.

Is it possible for A to create a tunnel to B and then for the user at B to
ssh back through that tunnel to A?

I was thinking that maybe the magical netcat
   http://freshmeat.net/projects/netcat
could possibly be used to accomplish this.

Any suggestions?
Thanks,
~M