Step 1: Open Microsoft Word 2007
Step 2: Click on the Windows Logo at the top left-hand corner.
Step 3: Towards the bottom right hand side of the drop-down menu, click on the button that says, "Word Options."
Step 4: When the "Word Options" windows opens, select "Save" in the left pane (this will bring up the "Customize how documents are saved" selection).
Step 5: Under the "Save Documents" heading, click on the drop-down menu next to "Save files in this format" and select "Word 97-2003 Document (*.doc)" from the list of choices.
From Now on, any file you save in Word 2007 will automatically be saved as .doc instead of .docx by default.
Bonus: If you are the type of Windows user that prefers creating new documents with the right-click menu, now you can create a Word 97-2003 file with the right-click menu using this registry hack (courtesy of the How-To Geek web site). Click on the registry hack to download the zip file. Then open the zip archive which contains 6 registry keys: the 3 "add<program>2003ToNewMenu.reg" registry keys will add Word, Excel, and PowerPoint entries to the right-click menu. The other 3 included keys will remove those items from the registry.
Step 1: Click on the "registry hack" link above and select "Open" (or "Open with...") from the menu to open the zip file in your default zip file viewer.
Step 2: When the archive opens, double-click on the registry key (e.g., AddWord2003ToNewMenu.reg), and select "Yes" to allow Windows to install the script to the registry.
Step 3: Right-click on the desktop or in a window and select the "New" sub-menu; you will now be able to create a new .doc, .xls, or .ppt file from the menu (you may be required to restart Windows before this takes effect).