(x,y) coordinates for grid.text()

 When using grid.text it seems my supplied (x,y) coordinates are being
 >  plotted only in npc (normalized parent coordinates) where (.5,.5) is the
 >  center of the graph.  How do I allow (x,y) to be coordinates corresponding
 >  to the (x,y) values in the graph?   The examples in ?grid.text seem to do
 >  this.  (I think the problem lies in how x and y are defined with respect to
 >  unit ).   Any help much appreciated.  Sample code below.

 Have you read the documentation for grid.text?  You need to read the
 description of the default.units argument and then read ?unit.