Oops! I misread and thought "opening pc files' on mac.
Unless confined to a certain, mac only app, the vast majority of mac files should open on a corresponding app on PC. As the above poster noted, make sure that the file has the extension shown - .doc, .xls, .ai, etc.
Using OSX 10.3.9 & 10.4.11 on a G4, G5 & Intel Macbook