Install doPDF:
http://www.dopdf.com/
Once it's installed, ANY program which has a 'Print' function available (such as Microsoft Word or any image viewing program) can be used to create a PDF. (You go to 'Print' and select doPDf as the printer. Obviously it doesn't actually print anything; it simply saves the file as a PDF).
So all you then have to do is to open the TIF file in an image viewer, and follow the instructions above.
Incidentally, unless you've got a particular reason for saving your scans in TIF format, it makes far more sense to save them as JPEGs. The files are much smaller. Further, you can send them by email - without even bothering to convert to PDF - confident in the knowledge that the recipients will be able to view them:
http://www.hp.com/united-states/consumer/digital_photography/organize_archive_photos/tips/scan_resize_share.html#3
Chris