File>Save as> Word 97-2003 Doc
When you are saving a file just do this:
In the 'Save files in this format' section, click the drop-down arrow and choose Word 97-2003 Document (*.doc).
Please everyone, don't discriminate!
More info
Save Word 2007 Documents as Older Version by DefaultFollow these steps to change Word 2007's default saving process. By changing the default setting, all of your Word 2007 documents will automatically save in the old Word version format.
1. Click on the Microsoft Office Button.
2. Click the Word Options button on the bottom of the window.
3. When the Word Options window opens, click Save in the left pane.
4. In the 'Save files in this format' section, click the drop-down arrow and choose Word 97-2003 Document (*.doc).