Cathi,

Well, it's not exactly trivial, but I guess it's not too long to post here. I'm assuming some familiarity with the article. For those who haven't read it, read it first.

To dynamically load your UserControl, use this code:

//use this if your UserControl is in the same web directory
this.MyControlHost.UserControlPath = "MyUserControl.ascx";

//use this if your UserControl is in another web directory
this.MyControlHost.UserControlPath = "~/MyDirectory/MyUserControl.ascx";

Here's the part I missed. This overridden property needs to be in your UserControl base class:

public override string UniqueID
{
    get
    {
        if (this.Parent.Parent != null)
            return this.Parent.Parent.UniqueID + "ctl0";
        else
            return base.UniqueID;
    }
}

And here's the DynamicControlHost ...

using System;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;

namespace YourNameSpaceHere
{
	public class DynamicControlHost : System.Web.UI.UserControl
	{
		#region Declarations

		protected string m_UserControlPath = "";

		protected System.Web.UI.WebControls.Panel WorkBox;

		#endregion

		#region Properties

		public string UniqueKey
		{
			get {return this.UniqueID + "DynamicControl";}
		}

		public string UserControlPath
		{
			get
			{
				if (this.m_UserControlPath.Length == 0 && Request.Form[this.UniqueKey] != null)
					this.m_UserControlPath = Request.Form[this.UniqueKey];

				return this.m_UserControlPath;
			}

			set
			{
				if (this.WorkBox.Controls.Count > 0)
				{
					// If a control is already instantiated, and it's not the same one that's
					// currently being requested, remove it before adding the new one
					if (this.UserControlPath != value)
					{
						this.WorkBox.Controls.Remove(this.WorkBox.Controls[0]);
						this.WorkBox.Controls.Add(Page.LoadControl(value));
						this.m_UserControlPath = value;
					}
				}
				else
				{
					this.WorkBox.Controls.Add(Page.LoadControl(value));
					this.m_UserControlPath = value;
				}
			}
		}

		public Control UserControl
		{
			get
			{
				if (this.WorkBox.Controls.Count > 0)
					return this.WorkBox.Controls[0];
				else
					return null;
			}
		}

		#endregion

		#region Page Init / Load

		private void Page_Init(object sender, System.EventArgs e)
		{
			// If it's a PostBack, change the ID of this control to what it was previously
			if (this.Page.IsPostBack && this.UserControlPath.Length != 0)
				this.WorkBox.Controls.Add(Page.LoadControl(this.UserControlPath));
		}

		private void Page_Load(object sender, System.EventArgs e)
		{
			// Put user code to initialize the page here
		}

		#endregion

		#region Web Form Designer generated code
		override protected void OnInit(EventArgs e)
		{
			//
			// CODEGEN: This call is required by the ASP.NET Web Form Designer.
			//
			InitializeComponent();
			base.OnInit(e);
		}
		
		/// <summary>
		///		Required method for Designer support - do not modify
		///		the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{
			this.Load += new System.EventHandler(this.Page_Load);
			this.Init += new System.EventHandler(this.Page_Init);

		}
		#endregion

		#region Methods

		protected override void Render(System.Web.UI.HtmlTextWriter writer)
		{
			base.Render (writer);
			// (char)34
			writer.Write("<input type=\"hidden\" name=\"" + this.UniqueKey + "\"value=\"" +this.UserControlPath + "\"/>");
		}

		#endregion

	}
}