If only one particular document is locked for editing, then open
the document and click on Tools | Unprotect Document.  If all new
and existing documents are locked for editing, then it's probably
because you have not activated your Word/Office software, or
because you have an expired trial version of Office 2003.  What
happens if you start Word and click on Help | Activate Product?
If you are already activated, a dialog box saying so will appear.
 If you are not activated, the Activation Wizard will start.  If
you have an expired trial version, a dialog box will prompt you
to enter a valid product key or purchase a key online.