Word is changing graphics resolution

For years I've been creating tiff graphics at 600dpi and inserting them in
Word docs with no problems. Recently when I save and close then reopen the
file, the graphics have been reduced in resolution. For awhile it seemed to
be irregular, but now it does it every time. When I first create the doc I
can print it and it looks great. I save, close, reopen and print, and the
graphics are all jaggy. I can't think of any change in my system or
software, except it migt have strted about the time I downloaded "Servcie
Pack 2." I'm not sure. I have hundreds of docs, thousands of pages,
including 2 camera ready books that are at risk. Thanks for any help.
(Currently using Word 2007 on a PC)
--
RHoffman