Sidecar info for bikes

People have mentioned the need/desire for a bicycle sidecar to bring a non-riding (injuried, sick, elderly, etc) friend along on a ride. Here are some ideas for the more mechanically inclined.

http://bikerodnkustom4.homestead.com/sidecar.html

http://bluecollarmtb.com/2005/05/06/bicycle-sidecar/

http://www.smokebikes.com/Sidecars.htm