public class Form1 : System.Windows.Forms.Form
	{
		 /// <summary> 
		 /// Required designer variable. 
		 /// </summary> 
		private System.ComponentModel.Container components = null;
		private System.Windows.Forms.Button button1;
		private System.Windows.Forms.DataGrid dataGrid;
		private System.Windows.Forms.Button button2;
		private System.Windows.Forms.Button buttonAdd;
		private System.Windows.Forms.Button button3;

		private Hashtable UserViewTable=new Hashtable();
............................
		private void button3_Click(object sender, System.EventArgs e)
		{
			User user=(User)this.dataGrid.BindingContext[this.dataGrid.DataSource,this.dataGrid.DataMember].Current;
			
			 //Проверяем наличия  в Hashtable объект(ключ) user 
			if(UserViewTable.ContainsKey(user))
			{
				object form=UserViewTable[user];
				 //Если форма не была создана или была закрыта 
				if(form==null||((Form)form).IsDisposed)		
				{
					 //Очистка мусора, т.к закрытая форма остается в памяти 
					if(((Form)form).IsDisposed)
					{
						GC.Collect();
					}
					form=  new ViewUser();
					((Form)form).Show();
				}
				else
				{

					((Form)form).Focus();
				}
			}

			else
			{
				Form viewUser= new ViewUser();
				UserViewTable.Add(user,viewUser);
				viewUser.Show();
			}
                  }
}