We would need to know the version number. Does the database file name have a file extension such as .FP5? If so, what is it? Do you have a copy of the original database that you can use to open the file?
Here's a knowledgebase article on file conversion you may want to take a look at: http://help.filemaker.com/app/answers/detail/a_id/750/kw/converting
History of Filemaker Wikipedia
1992-04 * FileMaker Pro 1.0v3 1992-10 FileMaker Pro 2 First Multi-platform (Macintosh and Windows) version 1992-11 * FileMaker Pro 2.0v2 1993-03 * FileMaker Pro 2.0v3