Unfortunately, it appears that Microsoft do not offer a Publisher reader. click here.
So it seems that Woolwell has the best solution.
Incidentally, I couldn't get Publisher 2007 to read and open files which I'd produced many years ago on Publisher 95, which is the opposite problem to that of Widdy!
If this is a frequent problem you might want to consider buying the latest version of Publisher (2010).
Why don't you download a free trial version? It lasts for 30 days, during which time you'll be able to open the files in question. If you don't want to buy the full licence at the end of the trial you should still be able to use it to open newer version files, but only to view them.