Hey Kenn,
Before I start I should just say that I’ve never done this, just working from my understanding. If you would like clarification or more advanced help we will have to wait for Andy or Steve later.
You should be able to open your backup database and export the relevant XXX_sftopics row and XXX_sfposts row’s and import them to your current database.
All entries in the ‘sftopics’ table have a topic ID, and all entries in the ‘sfposts’ table reference the unique topic ID that they belong to, so using something like phpMyAdmin you could select all the right posts using SQL commands (i.e, only show rows with topic ID of 1234..)
I’m guessing no users have been deleted? I think that’s the only thing that could cause a problem but again, never done this so just a rough idea of what to do more than anything!
Hope that helps, if not I’m sure Andy or Steve are not too far away.