pdf995.com has a freeware version (which is adware). The registered (non-adware) version is a whopping $10.
Either version should let you create PDF files. While I haven't used this program yet, the person who pointed me to this site sent me a PDF file he created w/ it and the file opened up fine for me in Adobe Acrobat. YMMV.
P.S. If this program lets you create PDF files the same way the full version of Adobe Acrobe does, you'll be able to PRINT your .pub file in MS Publisher to a "PDF Printer" (which will in turn produce your PDF file). This'll make it a little easier than using the PostScript/GSview/Ghostscript method mentioned in the previous message.