[dec]

Hola,

Prueba con algo así:

private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
	if(e.KeyChar == (char)Keys.Enter)
	{
	  MessageBox.Show("Pulsaste la tecla ENTER");
	}
}

private void button1_Click(object sender, System.EventArgs e)
{
	textBox1_KeyPress(this, new KeyPressEventArgs((char)Keys.Enter));
}