DataGrid - multiple select with no rowheader

Hi

I have customised the style of a datagrid so that the
rowheadervisible property is false. However, when a cell
is clicked I want the row to be selected (as would be the
case if the rowheader was selected).

How do you select select a whole row just by clicking one
cell and also allow multiple selections.

I have looked at extending the DataGrid class and
overriding the OnMouseDown event but I haven't been able
to achieve the required behaviour.

Any help much appreciated.

Thanks, Paul.