The Extended File Property PAGES is honored by PDFs but it doesn't appear to honor TIF, maybe there is another property that will though.

GetExtFileProperties() -
http://www.kixtart.org/forums/ubbthreads.php?ubb=showflat&Number=160880#Post160880

Also, here is a utility (never personally used it)
http://www.tucows.com/preview/517262/Tiff--PDF-Page-Counter-FREEWARE