Wireless Reflector for 802.11b?

Throgmorton's Nosehair asks: "My access-point and clients don't like talking to each other through multiple walls, even inside our single floor apartment. I already have a couple of the diddy 'range extender' antennas plugged into the client PCMCIA cards, but this is messy for laptops which are moved from place to place. The access-point has an omni-directional antenna. Is there any cheap-and-cheerful way to build a simple *reflector* (I'm already aware of the do-it-yourself directional antenna pages out there) to restrict the output to, say a 120-degree arc? I'm thinking along the lines of a sheet of cardboard covered with aluminum foil here (something that Blue Peter viewers could make with a cornflake packet, some sticky tape and a pair of scissors)." What are other ways that one can cheaply improve 802.11 performance in the home or home-office? Also, be aware that if you are improving the the reception on your signal that others may be listening in as well, so please take whatever steps you deem appropriate in securing your wireless LAN.