I want to execute a code when enter key is hit. I am using windows application in visual studio 2010/.NET 4. What event handler to be used here?

yes ...you can..

write a code what you want to execute on key press event..like

private void textBox1_KeyDown(object sender, KeyEventArgs ea)
            {
                if (e.KeyCode == Keys.Enter)
                {
                    MessageBox.Show("Enwter Key Pressed ");
                }
            }

you can call that event where you want..here i'm called in button click..

private void button1_Click(object sender, EventArgs e)
{
textBox1_KeyPress(sender, ea);
}
Thank you..
i hope this may useful for you..