I can’t believe that this works. I stumbled on this page and printed out a template. I got a piece of cardboard and traced the curve on it. Got a pair of scissors and tape then I placed it on my Belkin 54G antenna – and now, the signal in my room is now 3x stronger. I will post photos and a template of the cardboard reflector I made. You will just need a pair of scissors, a cardboard and tape.
Update: You can click the template above. Below, you can see what I came up with using cardboard and tape.