I hope this is the right spot:
Many forums have the feature to show new posts, with a little icon next to the post to show you that there is a new post. I find that not showing new posts defintely confuses the visitor, and I want to change that. What can I do to get around this?

This isn’t possible with the stock pMachine version.  pMachine does not track login/usage, so it has no way of knowing when a user was last online.  If you want that ability then you’ll need to add it yourself.  That would probably consist of adding code to set a cookie and checking when to update the cookie.

You’d then have to look at the cookie for the last login/active date whenever a user views the site and then display the “new” image for entries appropriately.

pMachine’s forum set is really only meant to be a basic forum (in fact, they’re really just regular weblogs that look like a forum).