Registration, spammers and such

[djsydeburnz]

I have searched a bit and figured I would ask here as I have not had any luck finding an answer.

I run a board that seems to be attracting alot of the spam accounts, not sure if it is happening everywhere, but it bugs me to no end.

Is there a way to set my site up so that it only allows registration for people that have been referred?

Or, better yet, is there any kind of mod out there that forces those wishing to register to fill out some type of application stating their intentions? I know this probably wouldn't totally solve it, but it might deter someone from joining if the process was a bit more in depth.

Thanks in advance.