How to check for user inactivity with and without platform invokes in C#

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;

namespace TestApplication
{
	/// <summary>
	/// Zusammenfassung f�r SomeOtherForm.
	/// </summary>
	public class SomeOtherForm : System.Windows.Forms.Form
	{
		private System.Windows.Forms.TextBox MyTextBox;
		/// <summary>
		/// Erforderliche Designervariable.
		/// </summary>
		private System.ComponentModel.Container components = null;

		public SomeOtherForm()
		{
			//
			// Erforderlich f�r die Windows Form-Designerunterst�tzung
			//
			InitializeComponent();

			//
			// TODO: F�gen Sie den Konstruktorcode nach dem Aufruf von InitializeComponent hinzu
			//
		}

		/// <summary>
		/// Die verwendeten Ressourcen bereinigen.
		/// </summary>
		protected override void Dispose( bool disposing )
		{
			if( disposing )
			{
				if(components != null)
				{
					components.Dispose();
				}
			}
			base.Dispose( disposing );
		}

		#region Vom Windows Form-Designer generierter Code
		/// <summary>
		/// Erforderliche Methode f�r die Designerunterst�tzung. 
		/// Der Inhalt der Methode darf nicht mit dem Code-Editor ge�ndert werden.
		/// </summary>
		private void InitializeComponent()
		{
			this.MyTextBox = new System.Windows.Forms.TextBox();
			this.SuspendLayout();
			// 
			// MyTextBox
			// 
			this.MyTextBox.Location = new System.Drawing.Point(0, 0);
			this.MyTextBox.Multiline = true;
			this.MyTextBox.Name = "MyTextBox";
			this.MyTextBox.ScrollBars = System.Windows.Forms.ScrollBars.Both;
			this.MyTextBox.Size = new System.Drawing.Size(288, 272);
			this.MyTextBox.TabIndex = 0;
			this.MyTextBox.Text = "";
			// 
			// SomeOtherForm
			// 
			this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
			this.ClientSize = new System.Drawing.Size(292, 273);
			this.Controls.Add(this.MyTextBox);
			this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedDialog;
			this.MaximizeBox = false;
			this.Name = "SomeOtherForm";
			this.Text = "SomeOtherForm";
			this.ResumeLayout(false);

		}
		#endregion
	}
}