Our company uses Office 2007 Professional Plus

How do you change the default date format?

I recently replaced a user's PC, and now the dates in his existing Word and
Excel documents are formatted with a four-digit year instead of two. This
has caused many problems with many of his documents, which need to be
reformatted to display correctly.

I have tried changing the short date configuration under Regional and
Language Options in Control Panel to M/d/yy. The dates on Excel sheets are
still displaying 4-digit years.