Don't have Microsoft Office?
"the leading open-source office software suite for word processing, spreadsheets, presentations, graphics, databases and more. It is available in many languages and works on all common computers. It stores all your data in an international open standard format and can also read and write files from other common office software packages. It can be downloaded and used completely free of charge for any purpose."
Have an older version of Microsoft Office? Can't open someone's attachment?
"Open, edit, and save documents, workbooks, and presentations in the file formats new to Microsoft Office Word, Excel, and PowerPoint 2007."
Do you have a file created in Works? Need to open it with Word?