If you use alt-F8 or alt-F11 and look at the Samples project of macros,
there's one in there that just simple text insertion for a function header
comment.  The Approximate Pseudocode is something like:
   sub InsertFileHeader ()
      ts as TextSelection = DTE.ActiveWindow.Selection
      ts.StartOfDocument
      ts.Insert("... my big string ...")

You could also use Tools->Macros->Start Recording and record typing in a
couple of lines of text after hitting ctrl-home and then going and editing
TemporaryMacro.  Rename it first to something you like because the next time
you record something, you'll clobber whatever is defined as TemporaryMacro.

Bill