How can I link the Joomla menu item ie. (automotive) to a Joomla forum automotive and how can I replace "the last post by xyz" with categories and sub categories.

Hi. I can't get what you are trying to say. Are you trying to create a menu link to a K2 item? Please be more specific.

Sorry, what I meant: I have a main menu (maximenu) set up in Joomla 2.5 with a bunch of sub-level items. I intend to install K2 and create a forum (just like this one). How can I link from a submenu item (i.e "Boating") to a particular K2 forum (category "Boating)? I'm new to both J and K2....

K2 is not a forum extension. K2 is a content extension. Apart that you can make K2 menu links to items, categories etc.