// Load a user control
MyControl userCtrl = (MyControl) LoadControl("~/Controls/MyControl.ascx");

// Or create an instance of your control
SubclassedControl subclassedCtrl = new SubclassedControl();

// Do stuff with controls here
userCtrl.LoadData();
subclassedCtrl.Text = "Hello World";

// Check which placeholder to add controls to
PlaceHolder placeHolder = (foo=="bar") ? placeHolder1 : placeHolder2;

// Add the controls
placeHolder.Controls.Add(userCtrl);
placeHolder.Controls.Add(subclassedCtrl);

<div id='rendercontent' style='display:none'>
  .. control here ..
</div>

<div id='newlocation1'><span></span></div>

<script language="JavaScript">
function replaceNode(newElementID, targetElementID)
{
    var targetElement=document.getElementById(targetElementID);
    var newElement=document.getElementById(newElementID);
    targetElement.replaceChild(newElement, targetElement.firstChild);
}
</script>

<script language="JavaScript">
replaceNode('rendercontent','newlocation1');
</script>

protected override void Render(HtmlTextWriter writer)
{
  AddAttributesToRender(writer);
  writer.RenderBeginTag(TagKey);

  writer.RenderBeginTag(HtmlTextWriterTag.Div);
  _control.RenderControl(writer);
  writer.RenderEndTag();

  writer.RenderEndTag();
}

Dim lblDisplay As Label = New Label()
lblDisplay.ID = "myLabel"
lblDisplay.Text = "Some Text"
pnlDisplay.Controls.Add(lblDisplay)