USR9106 port triggering

I have two programs (written in Delphi) which successfully send simple
TCP text messages to each other over a LAN using LocalHost on port
2000.

I'm now trying to get them to communicate over the Internet. My setup
is two computers connected to a USR9106 router/ADSL modem. I set up
port triggering in the 9106 software for port 2000 inbound and
outbound. I looked up the WAN IP (which is fixed) on the USR
software. I've read that NAT routing may not work with computers on
the same LAN, so I disconnected one computer from the network and
dialled in on it to my ISP. I checked from ipconfig that the dialup
IP address was different from the ADSL IP (in fact, only the last
block).

Then I gave the dialup IP as the host's IP address to the program
still running on the LAN and specified port 2000 for both programs.
But they wouldn't connect. The program attempting the connection to
the listening program reported an 10061 error (connection refused).

I also disabled the XP firewall and ZoneAlarm.

Can anyone please help me and suggest what may be going wrong ?