You'll be able to open the files with no problem as long as you have an appropriate program. eg, quark for PC can open quark for mac documents and vice versa. Same with pagemaker, freehand, indesign, office, and everything else I can't think of.
The problem is you won't be able to mount a mac volume. They'll need to burn a CD in iso format, so you can mount it.
Font's will also be an issue. If you don't have PC versions of all the fonts they used you'll have some major headaches.