To get this to work, I had to have phpBB2 and vBulletin in the same database.
Because when I tried to do the import with the following configuration
phpBB2 database: conversion_phpbb2
phpBB2 prefixes: phpbb_
vBulletin database: conversion_vbulletin
It tried to access vBulletin tables from the phpBB2 database (e.g. "smilies", "session", etc.) and I couldn't get anywhere.
Also, it didn't convert closed threads properly, and it stuck a thread that I didn't have stuck in the phpBB2 test forum. Just thought I'd let you know.
Pretty good effort, man. Thanks for this contribution to the vBulletin hacking community