I agree with the comment that altering a standard behaviour may confuse users. However to consume a keystroke you should set the SuppressKeyPress property in the KeyDown event handler, e.g.
private void TextBox_KeyDown(object sender, KeyEventArgs e) {
if (e.KeyCode == System.Windows.Forms.Keys.Back) {
e.SuppressKeyPress = true;
otherTextBox.Select();
}
}
Thats how it's done, but I do think you would be better off setting a sequential tab order for the TextBoxes and navigating between them using the Tab and Shift-Tab keys.
Alan