poof

Or try this.
On your computer, the one that works. Open your browser, type http://192.168.1.1, enter. Use no name and type admin as your password. Make sure dhcp is enabled, tell it how many users for dhcp, click apply.

In XP on the non-working machine, goto "my network places", (if you do not see "my network places, right click the task bar, click properties, start menu, customise, advanced, scroll down you will see it, check it). then "view network connections". Look at "local area connections", click on the connection you are using, at the "general" tab click "properties". You should see Client for microsoft networks, file and print sharing, tcp/ip, and QoS packet scheduler all installed with their little boxes checked. Your dads computer won't go without these things and XP should have installed them upon re-install, if the router or modem was connected at that time.

If they are not installed, install them using the tabs on that page. Or, goto "my network places", then click on "setup a home or home office network" and it will set up the before mentioned items.

If after asking XP to do it for you it still doesnt respond, do this. Turn off all the computers, unplug the modem power, unplug the router power.

IN THIS ORDER! Plug in the modem, wait untill all the display lights are lit on the front of your Surfboard (except activity), then plug in your router, then turn on the computers. That will make sure your nics, and the new network are recognised.

I hope this works for you, if not, well we can try something else.

edit: Had to shut off the parse url button.