Paul,
you probably install WF5 using several MB large installation manager. When your Internet connection is not very fast, then you are in troubles ... You need to get 4GB full installation package, but it is not available on www.ptc.com/appserver/auth/it/esd/academicFree.jsp page.
Try to ask academic support at academicsupport@ptc.com
-OR-
http://support.ptc.com/appserver/support/academic_case_logger/academic_case_logger.jsp
MH