1. The lack of exportability and readable access of MS Publisher files has long been a source of irritation for sole proprietor/micro and small business owners who used it in the late '90's and early 2000's to produced newsletters, brochures, etc. With each new incarnation of MSOffice, they have found themselves tied more and more to purchasing a later version of Publisher and ever increasing cost. In short, there is no other program that can open .pub files.
2. In the linux world there is an open source DTP program called Scribus.
3. However, even this has its own type of file system that can only be read by the program. To publish a finished article one must export to .ps, .svg or .pdf.
4. I understand that there is now an installer for Scribus on Windows systems.
5. Also see: http://goo.gl/gYMT9