The simplest way to set up a home network, including both computers with wired connections and computers with wireless connections, is to set up a wireless router immediately following your DSL modem or Cable modem. Sometimes, a DSL modem even has the router built into it.
In this setup, all the computers are assigned their IP addresses by the DHCP server that is built into the router. All are on the same logical network. However, their ability to share files, printers, and otherwise communicate between each other will depend on your settings in each computer.
In order to share files, you have to tell Windows (or Linux, etc.) to enable file and printer sharing, identify which directories should be shared, and have the computers on the same Windows Workgroup (or Windows domain, if you’re a very advanced user running a Windows domain controller). You’ll also have to tell the firewall programs on each computer to allow the sharing with the other computers — or the firewall will block the data.
A wireless router can be used along with a wired router, if you like. You can use it to add additional wired ports (wireless routers usually have 4 LAN (Local Area Network) ports as well as wireless ports. You can configure it so that you can share files and printers among the wired and wireless machines.
In order to have a combined network so you can share files and printers, you must only have one DHCP server running — either on the wired router or on the wireless router, but not on both. You will need to use an Ethernet cable to plug one of the LAN ports on the wireless router into one of the LAN ports on the wired Cable/DSL router.
In this one-network configuration, you will need to turn off the DHCP server that is built into the router. Although you don’t have to, you should set a static IP address in the wireless router, just so you’ll be able to find it with your web browser when you want to change its configuration.
Both of these steps will need to be done while you are directly connected to the router. Change the IP address to a fixed one, e.g. 192.168.1.254/255.255.255.0 on the wireless router, and assuming that the wired router’s DHCP server is assigning ranges in the 192.168.1.x range. Then, Disable the DHCP server in the wireless router.
Then, go back to the wired router and exclude the address (that you just assigned to the wireless router) from the range that the wired router’s DHCP server manages. Otherwise, you might find that the wired router assigned that address to another computer — which would interfere with the connections of that other computer and all your wireless computers.
Once all the connections work, don’t forget to set up the wireless security settings on your wireless router and your computer.