better wireless reception on mac p/book

I live in an old house with solid double brick walls and lots of rooms off a central passage - which translates into a wireless range nightmare. To top it off i am using a 18 month old aluminium powerbook (G4 1.67), whose wireless reception (via an built in airport card) is woeful. ??I am using a Netcomm NB5580W router. My brothers Acer laptop has access to the signal all over the house, so i know the issue is with the reception on the mac not the strength of the routers signal.??I want to have access to the internet all over the house, so which of the following options will give me the best range:
1) A high gain antenna e.g. Linksys HGA 7T or DLink Ant 0700
2) A PCMCIA card e.g. Sonnet or the Netgear (with an Orangeware 3rd party driver)

Thanks