The ~.tmp files created while you are working with a document should be
deleted when you close the document. If they are not deleted in the normal
course of events, then there is a problem. When Word crashes, however, many
temp files are left spread around (both in the document folder and in the
Windows Temp folder, so it is a good idea to have a good clear-out from time
to time. See
http://word.mvps.org/FAQs/AppErrors/LockedFiles.htm for some
general housekeeping recommendations.