Connect to several servers behind a router over internet

[benjamin@zbornikcity.de]

I am using VNC with several workstations in a LAN and it works very
well. Also connection through a firewall-router are working.

But now i have a little problem:

I assembled a network at a company with three workstations.

Workstation 1: 192.168.1.100 (Office1)
Workstation 2: 192.168.1.101 (Office2)
Workstation 3: 192.168.1.102 (Notebook)
Workstation 4: 192.168.1.103 (Fileserver)

Internet-Connection is over a WLAN-Firewall-Router (Linksys WRT54G)
with IP 192.168.1.1. The ports 5800 and 5900 are open for the use with
VNC and are forwared to all for IP`s of the workstations.

On every workstation the VNC4 Server is installed and starts at
power-on.

NOW THE PROBLEM:
How do i connect to the several workstation behind the firewall-router.
When i enter the IP of the router (e.g. 80.xxx.xx.xx) i always get
connected to the workstation OFFICE1 with the IP 192.168.1.100.

How can i specify when entering which workstation i want to connect
with?