View that shows posts specific to the node
You should begin around Views of course. Just make a taxonomy term per project, and use Views to create a page with all nodes of type "update(post)". Then in tpl.php for a texonomy field of "project info post", build a link based on taxonomy term. That's pretty much all.

Entity reference module is worth to look at, too. Using it you could relate all "update" nodes to "project info" node. Similar effect to taxonomy, has it's pros and cons of course. Read about both, and choose your poison - referencing node directly is cleaner way, but taxonomy seems to be supported better, and is in core so less contrib modules for you.

Last but not least - you could simply make the update posts a comments on project info post.