You can download available free edition of
Merge PST file Software. Using this software you can easily Merge MS Outlook PST Files and merge PST files into unique PST files. The software gives you and different option to join or merge PST on the basis of size, email id and a separate option to merge outlook contacts.
Read this tip for more details:
http://www.fixya.com/support/r267828...pst_files_into