customization of right click context menu is possible with word 2007. Following is the code
 
 Microsoft.Office.Interop.Word.Application app;
 app = (Microsoft.Office.Interop.Word.Application)applicationObject;
 CommandBar cellbar = app.CommandBars["Text"];
 CommandBarButton button = (CommandBarButton)cellbar.FindControl(MsoControlType.msoControlButton, 0, "MYRIGHTCLICKMENU", Missing.Value, Missing.Value);
             if (button == null)
             {
                 // add the button
                 button = (CommandBarButton)cellbar.Controls.Add(MsoControlType.msoControlButton, Missing.Value, Missing.Value, cellbar.Controls.Count + 1, true);
                 button.Caption = "My Right Click Menu Item";
                 button.BeginGroup = true;
                 button.Tag = "MYRIGHTCLICKMENU";
                 button.Click += new _CommandBarButtonEvents_ClickEventHandler(button_Click);
             }
 
 
 //handler for the button click
 private void MyButton_Click(CommandBarButton cmdBarbutton, ref bool cancel)
         {
             System.Windows.Forms.MessageBox.Show("MyButton was Clicked", "MyCOMAddin");
         }
 
 I hope you can get this working..
 
 Cheers
 
 Rajshree Dugar