I don't know much about Boost.Pool, but the documentation does say that it is header-only. You are probably including Boost.Threads somewhere in your program, or some part of Boost.Pool relies on Boost.Threads.
I see you're using MSVC. You need to have the Boost libraries in you library search path; the method for adding search directories depends on the version of MSVC you're using.
If you haven't built the Boost library binaries yet, take a look at this question for some tips.
Here's a good reference from Boost itself.
And this page from Mircrosoft will show you how to set your library directory. Use the link/dropdown at the top of the page to get specific instructions for your version of MSVC.