To the best of my knowlege, DataGrid will only let you do
anything on a row that has data behind it. What I do to accomplish
this is to always have one blank row at the end. The moment the
user makes a change it that row (starts putting data into it), I
create another blank row. Then when they save their data, I trim
the empty row off the end.
You could, feasibly, extend the DataGrid class and build the
functionality into it.