Limit # of connections per IP using ipfw?

[patrick]

Is there a way to limit the number of TCP connections from a
particular IP at a given time using ipfw? We are running Cyrus IMAP on
FreeBSD 6.2, and are sometimes subject to POP3 brute force login
attacks. I'm not sure if it's Cyrus or the SASL SQL plugin, but these
attacks grind the server to halt (the load level goes up beyond 350!).
The database against which authentication takes places is on a
separate server, so I know it's not MySQL's fault. I'd like to be able
to set a firewall rule to set a reasonable limit per IP for these
sorts of connections. I know that pf can do it, and I'm in the process
of figuring out how to migrate all of our stuff over to pf, but in the
meantime, I'd like to try to do this with ipfw.

Thanks,

Patrick