Hi Angel. I read your question and tought a little about it. I have some doubts about what exactly you're trying to do.
therefore it would be a good idea not to version control all of boost together with such projects.
Do you want to version-control Boost's sources within the Boost client project's repository? Since, for that project which uses Boost, Boost it's an external dependency (and you're not touching Boost's sources) I believe that the general recommendation is not to version control those sources. But, it is sometimes helpful to have in the same repository the dependencies so as to check-put the whole thing easily. What do you mean by repository? The whole one or just particular SVN project within a given repository. You may create independent subsets as different SVN projects, within a same repository. The future additions would be new, independent, projects. Then, each one checks out the project that he/she needs.
Can someone recommend a way to achieve this with subversion's branches-tags-trunk policy?
Trying to use tags/branchs/trunk, it seems that the concept of tag is closer to what you may need. In general, a tag is used to take a snapshot of the trunk and give a name to it. But it could be used in more ways. Take a look at this http://svnbook.red-bean.com/nightly/en/svn-book.html#svn.branchmerge.tags.mk... With this, you can make-up in your local workspace whatever a subset you desire, and then upload it to the repository with any name you want to use to identify it. I hope you find these comments useful. Rodolfo. -- Rodolfo Federico Gamarra