Sorry, I thought you were referring to a file in the current directory. All The Book Of Ruby programs have been tested with Ruby 1.9 by myself and a batch of editors and reviewers over the last 6 months in preparation for the 2nd edition of The Book Of Ruby from No Starch Press http://www.nostarch.com/boruby.htm
and they all work with very few changes (mainly to do with blocks and symbols); there is no fundamental incompatibility re. 'require'. You may want to verify that your system path is set up to the Ruby 1.9 directory. Otherwise, the only important difference with Ruby 1.9 require
is the one I mentioned before to reference files in the current directory.