dataGridResults.DataSource = MyDataTable;

DataGridTableStyle style = new DataGridTableStyle();
style.MappingName = MyDataTable.TableName.ToString();

DataGridTextBoxColumn fld1 = new DataGridTextBoxColumn(); 
fld1.HeaderText = "Job #";
fld1.MappingName = "JobNumber";
fld1.Width = 100;
 
DataGridTextBoxColumn fld2 = new DataGridTextBoxColumn();
fld2.HeaderText = "Client";
fld2.MappingName = "ClientName";
fld2.Width = 180;

style.GridColumnStyles.AddRange(new DataGridColumnStyle[] {fld1, fld2 });
dataGridResults.TableStyles.Clear();
dataGridResults.TableStyles.Add(style);