What version Office?
Office XP currently does not support the insertion of 16-bit/channel TIFF files
(64-bit CMYK TIFF files or 48-bit RGB TIFF files
To work around this problem, you can insert an 8-bit/channel TIFF image (32-bit CMYK
TIFF or 24-bit RGB TIFF).
To insert the image into Office XP, you must use a separate photo-editing program to
convert the image from a 16-bit/channel (64-bit CMYK TIFF or 48-bit RGB TIFF) to an
8-bit/channel (32-bit CMYK TIFF or 24-bit RGB TIFF).
There are many flavors of .tiff, Office generally uses .lzw
http://www.scantips.com/basics9t.html