Here is a method to add an item to the quick launch in C#

    private void AddNodeToQuickLaunch(string linkName, string SiteToOpen, string pathtoPage)
       {
           try
           {
               using (SPWeb web = SPContext.Current.Site.OpenWeb(SiteToOpen))
               {
                   web.AllowUnsafeUpdates = true;

                   SPNavigationNodeCollection nodes = web.Navigation.QuickLaunch;

                   SPNavigationNode createNode = new SPNavigationNode(linkName, pathtoPage, true);

                   foreach (SPNavigationNode node in nodes)
                   {
                       bool nodeExists = false;
                       if (node.Title.Equals("Lists"))
                       {
                           foreach (SPNavigationNode child in node.Children)
                           {
                               if (child.Title == linkName)
                               {
                                   nodeExists = true;
                               }
                           }

                           if (!nodeExists)
                           {
                               node.Children.Add(createNode, node);
                           }
                       }
                   }
                   web.AllowUnsafeUpdates = false;
               }
           }
           catch (Exception ex)
           {
               throw ex;
           }
       }