Server not accepting outside connectons for FTP..

OK, so clearly I'm doing something wrong. Here's what I've got going on:

On Server 2003 R2 -

I've enabled IIS/FTP services
Installed Filezilla Host (the server is active)
Set up a static IP
Forwarded ports 20 and 21 through my router
Set up users on filezilla host for the client connections.

Now, when I connect through the internal LAN - through one of the other computers in the office, everything's fine. But I can't connect externally..

Anyone know what's going on?

thanks in advance for any suggestions.