So, your ADSL works fine through the router (albeit wired)

You need to go into your wireless configuration on your laptop to connect to the router. You'll still need to sort out security settings on the router though. I'll hazard a guess that your dad's wireless network isn't running security....

What model no. is your router and what laptop, what operating system?

http://www.voyager.bt.com/faqs/wireless_index.htm