Hi,
If the FTP client is configured to run in PASSIVE TRANSFER MODE, the FTP server should be working even behind a NAT...
I have tried this with my current Freesco Linux Router (2.0 Kernel, mapping tcp:21 to an internal ftp server) and it works fine... but since I am a newbie in configuring Linux by hand (Freesco is really much simpler to configure for port forwarding), I haven't found the solution for E-Smith TCP port forwarding...
If someone can help me...