Thanks for the hint, unfortunately I have not gotten this to work yet. See
below.

The data grid object is given a DataSource (grid.DataSource =
someobject.FileList) which is an ArrayList of
objects with four members (FullName, Length, Extension, Name). Somehow no
matter what is put on the AddStyles there seems to be no coupling between
the two so that the grid is displayed with the correct proportions.

{
      :
     grid.DataSource = myObject.FileList;  // FileList is returns an
ArrayList, see above
     AddGridStyle(grid);
     :
}

private void AddGridStyle(DataGrid dg)

{

DataGridTableStyle ts = new DataGridTableStyle();

ts.MappingName = "FileData";

DataGridTextBoxColumn cs1 = new DataGridTextBoxColumn();

cs1.HeaderText = "FullName";

cs1.MappingName = "FullName";

cs1.Width = 170;

ts.GridColumnStyles.Add(cs1);

DataGridTextBoxColumn cs2 = new DataGridTextBoxColumn();

cs2.HeaderText = "Name";

cs2.MappingName = "Name";

cs2.Width = 80;

ts.GridColumnStyles.Add(cs2);

DataGridTextBoxColumn cs3 = new DataGridTextBoxColumn();

cs3.HeaderText = "Extension";

cs3.MappingName = "Extension";

cs3.Width = 20;

ts.GridColumnStyles.Add(cs3);

DataGridTextBoxColumn cs4 = new DataGridTextBoxColumn();

cs4.HeaderText = "Length";

cs4.MappingName = "Length";

cs4.Width = 20;

ts.GridColumnStyles.Add(cs4);

dg.TableStyles.Add(ts);

}