When you try opening a file that Mac OS X doesn’t recognize, it gives you the option to select an App on your computer that can open it. If you don’t have an App handy well, you’re out of luck.
However, when 10.6.6 comes out next week, you’ll have the option of searching the Mac App Store for an App that cn open those pesky files. 9to5 Mac obtained some leaked screenshots which show that when the App Store comes to the Mac, it’ll give you the option to search for an App to deal with hard to open files.