1) Use grid.CurrentCell.MoveTo to set the current cell to a particular row and column. If you are trying to do this from Form-Load, also set grid.ForceCurrentCellMoveTo = true;
2) In the grid, the default values come from GridDataBoundGrid.Model.ColStyles[col].CellValue. So, in your formload, if you have the DataTable.Columns[col].DefaultValue's, you could move them into the ColStyles.
Here is a little sample showing how you might do it.
But if you want to dynamically set the values without relying on the defaults in the DataTable, try handling CurrentCellMoved.
private void gridDataBoundGrid1_CurrentCellMoved(object sender, GridCurrentCellMovedEventArgs e)
{
GridCurrentCell cc = this.gridDataBoundGrid1.CurrentCell;
if(cc.RowIndex == this.gridDataBoundGrid1.Model.RowCount)
{
this.gridDataBoundGrid1.Binder.BeginEdit();
this.gridDataBoundGrid1[cc.RowIndex , 1].Text = "defaultcol1";
this.gridDataBoundGrid1[cc.RowIndex , 2].Text = "defaultcol2";
}
}