Hardware Install - this is pretty easy, the hardware should be plug and play.
1) Install a Network Interface Card (NIC) into any computers that don't have an ethernet connector following the instructions that come with the hardware.
2) Run a "straight through" Ethernet cable from the router to each computer.
3) Turn everything on and make sure you get 4 green lights (LEDs) on the router. Note if you have an older router or NIC one or more lights may be yellow indicating a low speed connection. If you get 4 lights your cabling and hardware is good. If not check the cables that go from the computer to any LED that is not on.
Software Install - The easiest way for beginners is to use the Wizard. The following steps need to be done for each computer:
Turn on all the computers and printers.
1) Go to Start, select Help and Support, in the search box type NETWORK WIZARD and hit enter.
2) Click "Add a Windows XP Computer to your Network"
3) Read the instructions in the box that opens on the right. Ignore the part about Internet Connection Sharing ICS (we'll do that later after the local network is working).
4) When ready click the highlighted blue line that says Network Setup Wizard. Now just follow the instruction. If you get lost just start over.
-When asked how your computer connects to the internet select the "Other" button then select "This computer connects to a network that does not have an internet connection."
-Give each computer a name, any names work Bob, Ted, Carol & Alice. Den LivRoom, Kitchen, Bedroom, etc. You can leave the description blank.
-Workgroup name must be the same on all 4 computers. It defaults to MSHOME. It's more secure to give it a new name SAZARFOLLY or anything you like. just make sure it's the same on all 4 computers.
-Ignore the part about making a network disk.
-You will still need to install the printer drivers on any computers that are not connected directly to the printer. You can use the disk that came with the printer or let windows "find a driver".
You are done with the basics now and should be able to see each computer's shared directory and printers on the other computers.
Additional Sharing Setup - this can get a little annoying because Windows tries to hide your data for your protection.
-Initially only stuff in the directory called "Shared Documents" is visible to other computers on the network. These shared directories will show up as "ShareDocs on (name of the computer)" under My Network Places.
-You can make additional directories visible to other computers also by right clicking on the folder and selecting "Sharing" on the menu.
-You can even share CD and DVD players over the network this way.
Firewalls - if you have software firewalls installed they will block access to the other computers on the network and must be configured to allow access over the LAN.
SAZAR - good luck. As I worked on writing this I decided you are very brave or very foolish for volunteering to help without physical access to the machines.
EDIT- Consider having her setup the machine that will have the modem and be the gateway to the net first so you can take remote control and then walk her through it on that machine. Maybe she can get the rest after that.