You should be able to access the controls using the FindControl method.

for (int i = 1; i <= 5; i++)
{
  Label label = new Label();
  label.ID = "Label" + i;
  label.Text = "Label" + i;
  form1.Controls.Add(label);
}

((Label)form1.FindControl("Label1")).Text = "Hello, Label 1!<br/>";
((Label)form1.FindControl("Label2")).Text = "Hello, Label 2!<br/>";
((Label)form1.FindControl("Label3")).Text = "Hello, Label 3!<br/>";
((Label)form1.FindControl("Label4")).Text = "Hello, Label 4!<br/>";
((Label)form1.FindControl("Label5")).Text = "Hello, Label 5!<br/>";

HTH.

-dl

--
David R. Longnecker
http://blog.tiredstudent.com