Active FTP in IAG 2007

Hi,
I have an application that basically run ftp, change to a directory,
download a file(s) to the client computer.
The application work with any VPN(Microsoft Remote Access, Checkpoint
SSL,etc)
Now we start using IAG 2007 appliance to simplify the conections to the
users as a single sign on point for all of our applications.
I manage to get working Web, Sharepoint, Outlook, Telnet applications, but
FTP(Active) is giving me a headache.
I manage to open an FTP session to the internal server, but when I send a
command (ie. dir) it is not successful, since the port is changing after the
initial conection to port 21(FTP).
Does anyone know the correct configuration for the application? FTP (Active)