Build it using the instructions in the Getting Started section of the index.html file in the root directory of the downloaded Boost sources. Specifically section 5.2 with gcc as the toolset.

OR

Read the same instructions on the Boost web site:
http://www.boost.org/doc/libs/1_45_0...ted/index.html

OR

Search this forum, this question has been asked and answered before:
http://www.qtcentre.org/threads/3584...ighlight=boost