using System.Runtime.InteropServices;

[DllImport( "user32.dll" )]
public static extern int GetWindowText( IntPtr hWnd, StringBuilder lpString,int nMaxCount );

[DllImport( "user32.dll" )]　　
public static extern int GetClassName( IntPtr hWnd, StringBuilder lpString,int nMaxCount );

[DllImport( "user32.dll" )]　　
public static extern IntPtr WindowFromPoint(Point point);

int x = Cursor.Position.X;
int y = Cursor.Position.Y;
this.textBox4.Text = string.Format( "({0},{1})" , x, y);

Point p = new Point(x,y);
IntPtr formHandle = WindowFromPoint(p);
this.textBox1.Text = formHandle.ToString();

GetWindowText(formHandle,title,title.Capacity);
this.textBox2.Text = title.ToString();

StringBuilder cllassName = new StringBuilder();
GetClassName(formHandle,cllassName,cllassName.Capacity);
this.textBox3.Text = cllassName.ToString();

this.timer1.Enabled = !this.timer1.Enabled;