Help with phpbb board conversion

[Alanmelon]

Hi, having been a bit stupid, when converting an old phpbb board into a new smf install I've done things around the wrong way, to keep it simple, here's my problem;

1) I set up a significant amount of new categories and posts on a new installation
2) I backed up this database prior to running the phpbb convertor to import old posts and users from an existing forum, which obviously overwrote all of my hard work in 1.

How can I use my backup to add back the categories and posts from step 1, whilst retaining the converted data? I'm assuming some SQL queries are going to be in order so some specific help would be much appreciated.