i think i understand what you are trying to do. In order to use the old router as a simple hub to add more ports to your network, you need to log into it and turn off DHCP... you cannot have more then 1 device on any network serving DHCP - assigning IP address to devices that connect to the network. If you do, bad things will happen ^^
This is pretty easy especially since you say you reset the device. Turn it on and plug a single computer into it. On the computer go to [Start] [run] then type cmd into the run prompt. (on windows 7 there is no button for "run" just type cmd into the big box at the bottom of start menu.
Once the black window of the command prompt comes up, type in ipconfig/all
and see what it gives you as a "default gateway" if there isn't one and your "IP Address" starts with 169 the router is not broadcasting DHCP, and you may use it as is (do not use the "internet-connection-goes-here port" just the local network ports
If you do a see a default gateway, it will most likely look like 192.168.xxx.xxx
take those numbers and feed them into your internet browser - that should send you straight to the management interface of your router. Default passwords for most devices are usually "Admin" or some variation thereof. Look up your make and model up on Google, it will not be hard to find it.
Then you will need to browse the interface to find where you can turn off DHCP - usually some section that deals with local network setup. depending on what you want to do, you may also want to turn off or adjust wireless settings.
Happy hunting and good luck!