banning by IP doesn’t always help because they tend to use spoof IP’s so you ban them today, and they use a new IP tomorrow.
Forcing activation by email seems to help some, because alot of them used to use fake email addresses, and that got rid of lots.. banning *mail.ru and *cashette.com helps quite a bit in my forums. I also work for a few forums here, and have noticed that those two emails seem to be repeat offenders just about everywhere, by the time i realized the trend I had about 100 members with those email addresses that I had banned by IP.
I’m also very interested in the mod, and do use a couple phpbb forums, going to check that out now 
Anyone know if VB or IPB has a simular option?