(EX. If the old laptop IP is 192.168.1.2 make the new laptop 192.168.1.1) Fill in the subnet mask (Which should be 255.255.255.0) and the default gateway listed. (Most likely 192.168.1.1 as this is the default router IP in most cases) Then you should be good.
If the router is using the default IP scheme then 192.168.1.1 is most likely the address of the router, making the new laptop this address would cause conflicts. I would think you want to make the new laptop(s) 192.168.1.3 and 192.168.1.4 and set the default gateway at 192.168.1.1. This is assuming a fixed IP scheme.
You may want to just go back to the basics.
Get the setup guide for the router.
Set the router back to its default settings, there should be a small button you push and hold in with a pen or tooth pick or any think small that will reset the router back to it's factory defaults.
Follow the setup guide to setup the router and connect all the pc's
Most likely you will be able to connect right in with the new laptops, your old laptop may need to have a new connection setup if the old was using a fixed address or wep.
Once you have all your computers connected and working then go back and setup any security you want, admin password on the router, wep or simple mac filtering, either work fine.
Routers are fun, aren't they! :eek2: 
