Looking for a way to deter spammers from forum boards . . .

Hey guys. M forums have been getting majorly bogged down in spam members lately.
I have already set up the process where I have to confirm everyone that comes in, so the spammers can't post (except in my "problems" forum, which has to be public).
I'm just looking for a way to block the spammers from signing up at all.
I use free phpbb, and can't really use much else because I don't know much about transferring all of the posts to another forum type. I can't afford to lose the posts I have, and I archive often.
I'd like my forums to us this setup, as vBulletin is pretty nice and nicely customizable. Granted, I need to know more php to be able to do anything more anyway.
If someone can tell me how to block spammers or transfer to a better forums program, it'd be MUCH appreciated!
Deleting spammers blows.

Jam it back in, in the dark.

Thanks guys.
I have captchas enabled, and I also have an admin that helps me delete members. Mods can't delete members in phpBB. Yeah. Lame.
I do like SMF, and if there's a converter, maybe I'll just do that.
Thanks for the help guys!
Keep those suggestions rolling in though! I like a wide variety of optios when making a big decision such as this.
I'm just afraid I'd lose my current list of members, as most transfers lead to members having to re-sign. I hate that. Building from scratch when I've worked so hard to get where I'm at. You know what I mean GFF . . .
Heh.

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