How to Colonize an Asteroid
The ship which will carry the colonists and their supplies to the asteroids will have to be constructed in the form of separate modules here on earth. No rocket in existance could launch anything as big as the finished craft will be.
Modules currently being designed by many different nations for use on the international space station would be good building blocks, and could be redily adapted for use in the colony ship. Some form of superstructure or fuselage would have to be developed to bind the modules into a group. In addition, the colonists might want to send out an unmanned cargo ship filled with supplies and heavy equipment before sending themselves.
Any modules or assemblies will have to be designed with currently available technology in mind, such as NASA's space shuttle, the Russian "Proton", or other heavy lift launch vehicles currently under construction.