INX files can be opened by CS:
http://www.istockphoto.com/forum_mes...d=56384&page=1
Remember to resolve any font or image issues before you save to INX. INX is actually an XML file, a representation of your INDD file not an exact copy. That's why they crash much of the time.
If you limit any CS3 features in that file, that will also improve your chances to back save.
And more here:
http://creativebits.org/indesign/ind...rchange_format
And from Adobe, more about CS3 and INX:
http://www.adobe.com/support/downloa...jsp?ftpID=2448