private void button1_Click(object sender, RoutedEventArgs e)
{
    int rowIndex = 0;
    int colIndex = 1;
    // 行、列の番号を指定してDataGridCellを取得する
    DataGridCell cell = GetDataGridCell(dataGrid1, rowIndex, colIndex);
    // データグリッドセルにフォーカスする
    FocusManager.SetFocusedElement(this, cell);
}

public DataGridCell GetDataGridCell(DataGrid dataGrid, int rowIndex, int columnIndex)
{
    if (dataGrid.Items == null || dataGrid.Items.IsEmpty)
    {
        return null;
    }
    DataGridRow row = GetDataGridRow(dataGrid, rowIndex);
    if (row != null)
    {
        DataGridCellsPresenter presenter = GetVisualChild<DataGridCellsPresenter>(row);
        DataGridCell cell = (DataGridCell)presenter.ItemContainerGenerator.ContainerFromIndex(columnIndex);
        if (cell == null)
        {
            // Visual Treeが構築されていない場合もあるため更新
            dataGrid.UpdateLayout();
            dataGrid.ScrollIntoView(row, dataGrid.Columns[columnIndex]);
            cell = (DataGridCell)presenter.ItemContainerGenerator.ContainerFromIndex(columnIndex);
        }
        return cell;
    }
    return null;
}

public DataGridRow GetDataGridRow(DataGrid dataGrid, int index)
{
    if (dataGrid.Items == null || dataGrid.Items.IsEmpty)
    {
        return null;
    }
    DataGridRow row = (DataGridRow)dataGrid.ItemContainerGenerator.ContainerFromIndex(index);
    if (row == null)
    {
        // Visual Treeが構築されていない場合もあるため更新
        dataGrid.UpdateLayout();
        dataGrid.ScrollIntoView(dataGrid.Items[index]);
        row = (DataGridRow)dataGrid.ItemContainerGenerator.ContainerFromIndex(index);
    }
    return row;
}

public static T GetVisualChild<T>(Visual parent) where T : Visual
{
    T result = default(T);
    int childrenCount = VisualTreeHelper.GetChildrenCount(parent);
    for (int i = 0; i < childrenCount; i++)
    {
        Visual child = (Visual)VisualTreeHelper.GetChild(parent, i);
        result = child as T;
        if (result == null)
        {
            result = GetVisualChild<T>(child);
        }
        if (result != null)
        {
            break;
        }
    }
    return result;
}

<Window x:Class="WpfDataGrid.BindingWithViewModel.TestWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="TestWindow" Height="300" Width="300" Loaded="Window_Loaded">
    <Grid>
        <DataGrid AutoGenerateColumns="False" Height="200" HorizontalAlignment="Left"
                  Name="dataGrid1" VerticalAlignment="Top" ItemsSource="{Binding DataTable}">
            <DataGrid.Columns>
                <DataGridTextColumn x:Name="Column1" Binding="{Binding Path=col1}" Width="100" />
                <DataGridTextColumn x:Name="Column2" Binding="{Binding Path=col2}" Width="100" />
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>

using System.Data;

namespace WpfDataGrid.BindingWithViewModel
{
    class ViewModel
    {
        public DataTable DataTable { get; set; }
    }
}

using System.Windows;
using System.Data;

namespace WpfDataGrid.BindingWithViewModel
{
    /// 

    /// TestWindow.xaml の相互作用ロジック
    /// 

    public partial class TestWindow : Window
    {
        public TestWindow()
        {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            DataTable dt = new DataTable();
            dt.Columns.Add("col1");
            dt.Columns.Add("col2");
            dt.Rows.Add("1", "One");
            dt.Rows.Add("2", "Two");
            ViewModel vm = new ViewModel();
            vm.DataTable = dt;
            DataContext = vm;
        }
    }
}

Dim key As Key = Key.Insert
Dim target As UIElement = Keyboard.FocusedElement
Dim routedEvent As RoutedEvent = Keyboard.KeyDownEvent
Dim e As KeyEventArgs = New KeyEventArgs(
                            Keyboard.PrimaryDevice,
                            PresentationSource.FromVisual(target),
                            0,
                            key)
e.RoutedEvent = routedEvent
Grid1.RaiseEvent(e)

Dim params As HwndSourceParameters = New HwndSourceParameters()
Dim source As HwndSource = New HwndSource(params)
Dim k As Key = Key.A
Dim e As KeyEventArgs = New KeyEventArgs(Keyboard.PrimaryDevice, source, 0, k)
e.RoutedEvent = routedEvent
Grid1.RaiseEvent(e)