You don't mention the version of Word you are using.
For 2003 and prior, Tools, Language, Hyphenation, uncheck the "Automatically
hyphenate document".
For 2007 I am not exactly sure where you will find this control, do a search
for hyphenation.
If this problem is occuring in all you new documents, you may need to open
the normal.dot and take of the hyphenation there, as well as in the
individual files.
Hope this helps
DeanH