In Word 2007 a lot of things have been changed since word 2003. For instance the file menu is no longer present, it has been replaced by a glowing yellow button which is the office button. If you click on this button, a menu will pop up. In this menu click the save button. It'll give you the option to save your document with a docx extension. The problem with this is that a file with this kind of extension does not open in anything but Word 2007. Instead go into save as and save it as a word 97-2003 document. In case you want to make this change permanent, go back into the office button then into word options, here click on the save tab and change the save file format from docx to word 97-2003. Now it will always save this way by default.