Hi,
Can you at least log into your NATed ftpd? If you can log in,
but no files come through, then this very likely issued by
FTP's seperate data connection [1]. 

On active FTP the client opens a port (breaks if the
client is behind non ftp-proxying NAT) for data transfer.

On passive FTP the server opens the port (breaks when the 
server is behind NAT).

AFAIK you may run a passive ftpd behind NAT, when you set 
a specific portrange for the data connections and redirect
those. 
Each modern ftpd should be able to do this. From the tnftpd
ftpd.conf(5) man page:

portrange class [min max]
Set the range of port number which will be used for the passive
data port.  max must be greater than min, and both numbers must be
be between IPPORT_RESERVED (1024) and 65535.  If class is ``none''
or no arguments are specified, disable this.

HTH

-Alex (behind NAT and quite happy with passvie FTP)

[1] http://slacksite.com/other/ftp.html