I had been using WordPerfect for publishing on a PC in the early 1990s. After I moved over to the Mac, I thought I would not be able to access them again unless I spent a prohibitive amount on MS Office for Mac. I have been using the free NeoOffice instead, which not only allows me to exchange files with MS Office users (including collaboration and annotation), it can also read all my old PC-based MS Office files. (Apparently this is not always easy with Mac Office.)
In addition, I can also access all my old WordPerfect files again.
[robg adds: A previous hint discussed using NeoOffice to read PowerPoint files.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060218025726828