Взгляните на этот образец:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
this.MouseDown += new System.Windows.Forms.MouseEventHandler(this.Form1_MouseDown);
}
private void Form1_MouseDown(object sender, MouseEventArgs e)
{
TextBox tb = new TextBox();
tb.Location = new Point(e.X, e.Y);
tb.Width = 100;
this.Controls.Add(tb);
}
}