1. You should be able to use Review tab | Compare | Combine. This command combines revisions from several authors into one document. Modifications become tracked changes in the resulting document.
2. Filenames don't have to the identical. Personally I find it easier to work with different filenames, because it is easier to tell the source documents apart.
See also
http://office.microsoft.com/en-us/wo...132.aspx?CTT=1.