If you are talking about pulling a trailer with your bike then you need to look at the delphi group called Motorcycle trailer pulling forum.
It can be found here on this link http://forums.delphiforums.com/MCTrailertowing/start
You will need to register but no cost for basic membership. There are lots of people that can answer most any question you have about pulling.
That being said I pull a home made trailer. It is based on a harbor fright kit trailer that has 8" wheels and is approximatly 4x4 in size. I have added a diamond plate shiny aluminum box to it and painted the frame. I also added LED lights to the mix. I have about 600 dollars into it and it works great. I use a Kurykyn hitch and a hoppy converter to adapt my HD wiring to the trailer. I have pulled it on three different trips and last summer we put over 3000 miles on with the trailer in tow. There are a lot of people on the trailer forum that use car top carriers for the box on the trailer kits.
If you would like to see my trailer it can be seen here http://photobucket.com/albums/v60/Rickb/Trailer/
Like I said it is home made and pulls like a dream.