Converting documents on Word 2007 to Word 2003

Most of the word files I am receiving right now are from Microsoft Office Word 2007 that has .docx or .docm extension. I only have Microsoft Office Word 2003 on my pc that is why I’m unable to open them. I don’t want to upgrade yet to Office 2007 because Office 2003 is still working for me.
There might be a simple program that I can install so I will be able to view Word 2007 documents. Upgrading will be costly I think. It would be of great help if you can suggest one for me to install for free.
