Router changing ip's on lan

i have a d-link ebr2310 4 port wired router and it usually works great. for the computers on the lan, lets call em #1 and #2. #1 is the one that was originally used for setup and lets say its ip ends in .090 and all port forwarding is using that ip and the correct ports, but when i go to #2 machine it shows all my port forwarding as .090 - it does not keep .091, i can set it right and when i go back to #1 it has #2 ip, for port forwarding, i can change it each time but its a pita, it used to not care what machine i was on as long as it was part of the lan. how can i declare a range of ip addys to allow me to work on all of my machines. thanks a lot!!!

 

You probably need to set a static IP for both PC's. I have the same router and have done that with both my PC's. Here is a good tutorial on doing that if you use XP. http://www.portforward.com/networking/static-xp.htm
Edit: Not knowing your OS I have added the page that allows you to pick the OS you have and then takes you to the proper set up page
http://www.portforward.com/networking/staticip.htm

 

Take a good look at the DHCP menus, some Router let you set Static IP within the DHCP.

In such cases the computer's TCP/IP stays on Auto Obtain IP, and it obtains its IP from the Router's DHCP, but the IP would be always the same. If your Router has this feature there would be a menu to enter the computer's MAC address.

Otherwise you have to set a regular Static IP in the computer. This Static IP has to be out of the DHCP range.