So now your Windows computer is connectng to the router and getting on to the net no problem. Unless you had to actually type an IP address into your computer, it means that the router is assigning an ip address to your computer. If you go to a command prompt and type ipconfig, you will proobably see an ip address like 192.168.xxx.xxx

Your Dad's MAC is probably not being assigned an IP addrss by the router because it is configured to get an IP addrsss from the ISP. If you are using ADSL, which is high speed through the phone lines, then that is not the same as TCP/IP. Your Dad's Mac probably needs a configuration change to work with DHCP, which is a form of TCP/IP. All this is assuming your Dad's MAC is now plugged back into the router.