I'm electing Wei Wei as the new moderator. He/She or whatever the hell it is, is in here more than you. and with all the WoW gold he has been selling, I bet he can afford to buy an R8 and become more involved.
Perhaps instigating an activation email procedure as part of initial registration would be a good plan. I'm sure we'd all be ok re-registering to not have spammers polluting the forum.
A friend of mine runs a couple of music forums and has found this the best way to keep the automated spam at bay... he gets around 150 bounced emails each day from fake registrations.
There has been masses of spam of late - with the spammers creating new usernames and spam bombing 5-10 old threads with garbage links to their wow gold sites. The moderators have cleaned up the old threads and hopefully the email confirmation they've added will mean this site won't be as prone to the scripts the spammers are using.
Saw the spammers have just posted a batch again - I'd strongly recommend changing to a non-standard captcha or something like a simple sum type approach where you present 2 numbers and a function (add/subtract) and require a human answer.
the problem with using standard built in vb stuff is the scripters get the best return on effort for defeating those as that gets them into a large number of sites vs having something unique to your site which would require them to specifically target you rather than the scattergun approach they typically use.
My friend just has a set of numbers written in text on the 'About' page. When you register, it tells you to go to the page and get the numbers. Bots can't do this. There is never any spam on his board.