But I'm not sure if newer versions follow the same installation path form. If you're reading this and you have MS Word, could you please reply and specify what version of Word you have installed and its installation path?
Another possible approach is to look in the registry.
Look for .doc under HKEY_CLASSES_ROOT and see which application is registered to run it.
The value stored is a key which Windows somehow uses to find the application path.
On my computer the default value shows Word.Document.8 and I have Office 2003.