You can do something like this
SPNavigationNodeCollection nodes = web.Navigation.QuickLaunch;
for(int i = nodes.Count - 1; i >= 0; i--)
{
//this will let you access all the nodes available in a quick launch using nodes[i]
}
see this link also: http://www.mtelligent.com/journal/2007/10/7/customizing-the-quick-launch-menu-with-spnavigationnode-spna.html
Hope this helps