Using VNC or XP Remote Desktop behind router

Hi, I am new. I an trying to run VNC or XP's Remote Desktop so I can remotely control my home computer. But here is the problem.

I am using cable modem and have three computer hooked up with a Siemens SpeedStream 2614 router. So we only have one public and 3 private ip. But VNC and XP Remote Desktop require an IP to access.

I search a while and see all the people talking about opening ports and port forwarding stuff. But I dont know how to do them.
Would someone help me?

 

I don't know about the specifics of configuring your router, since I don't use one of those. I use VNC (actually tightVNC), for remote support of clients, and it works well through several flavors of routers. You have to open ports 5800 and 5900 for a standard installation, if you have more than one PC to access behind the firewall, then the numbers go up 5x01 = PC 01, 5x02 = PC 02, etc.