Good point about the DNS. If she is not on a domain.
I also agree, set up static IPs, especially on the main computer.
Control Panel -> Network Connections -> Local are connection -> right click on the NIC (usually two blue computers -- if connected, if not then grey) -> choose properties -> click on TCP/IP in the middle window. There click on Use the following IP address and put in the information.
You can find the information you are currently using at a command prompt by typing: ipconfig at the command prompt.
Personally, I would make them all static. That would override the DHCP on the router anyway but, for best practice, I would turn that off. Using a DHCP server is really best for a network and a server giving the IPs out. There are advantages to using dynamic IPs with a DHCP, but it isn't that much of an advantage over static.
So, in a nutshell and agreeing completely with Paul, just give all of the computers static IPs.
