To solve this annoying problem, there are a few options available:
- Download OpenOffice, an alternative to Microsoft Office
- Send the document to me and I will convert it for you from docx to doc format
- Buy Microsoft Office 2007 - not recommended unless you have a fat wallet.
It all stems from Microsoft's decision to change the default document type in Office 2007 when saving a Word document as .docx format. It used to be .doc format e.g. Shopping_list.doc but would now be saved as Shopping_list.docx. Since most of the world and his dog use versions of Microsoft Office 2003 or earlier, you won't be able to open it. Ridiculous logic but then that's Microsoft.
My recommendation would be to use the open source product OpenOffice. This suite of applications is able to open the new file formats (XML based) such as .xlsx (Excel) and .pptx (Powerpoint). You can then save the document in .doc/.xls/.ppt format. Personally, I use both Office 2003 and OpenOffice. That way, I am able to open any of the newer file formats and still be able to use (in my view) the infinitely superior Office 2003 suite - compared to the nasty Microsoft Office 2007 suite.