A Funky Tree

Hello - I'm currently a sophomore in college studying computer engineering.  I love learning, but web development is somehow magnetizing for me.  I've done some generic searching but I can't reduce my issue into search-friendly terms, so I figured I'd ask here.  Skip to the bottom for a CliffsNotes version of my question. 

I think my issue would best be shown with an example: 

Say I have a "node" of information, all pertaining to, say..cars.  Each node represents a specific car, with defining characteristics (color, manufacturer, top speed, etc).  Say I have a website centered around cars; the homepage gives the user several viewing options.  The user can sort the "nodes" in several levels - he can view all cars that have "red" in the *color* value of the node, or he can navigate further down into "Red" > "Aston Martin" > "Vanquish".  Say he wants to start with the manufacturer:  "Aston Martin" > "Vanquish" > "Red".  This sorting algorithm seems simple enough, but say I want to append a forum topic at each level. 

So each color would get a forum, followed by a list of references to more specific criteria.  I'm thinking about the implementation of a tree-structure, with each level of the tree having it's own forum.  The lowest level (the "leaves") also have forums.  After looking over some of the php files in the PunBB .zip, I'm not sure exactly how to go about implementing this dynamic nodal-forum. 

I'm also thinking about creating an array of nodes, and having the sorter simply "crawl" the array every time a user wants to sort/narrow down the displayed "nodes" more. 

Would you say that it's more efficient to modify this code to satisfy this array-based nodal-forum, or should I start from scratch?  I know this is pretty general, but any advice would be great.  Thanks!