Install the Microsoft Office Compatibility Pack for 2007 Office and any necessary Office updates. By using the Compatibility Pack for the 2007 Office system, you can open, edit some items, and save Office Word 2007 documents in previous versions of Word.
http://office.microsoft.com/en-us/word/HA100444731033.aspx

you have received one answer...the other way that i have been more considerate of is to as a Office 2007 user to automatically save the files as a Word 2003 format.

You can ask the sender to send them to you in 2003 format. Them to do "Save As" option.

Or Microsoft has a Word 2007 viewer for free if you just want to view.

Or if you don't want to install anything you can convert your documents online at www.docx2doc.com or www.convert-doc.com