If you'd rather not use a dll, this ought to do what you want.
Code:
on *:JOIN:#chanX: {
  msg #chanY 14* Joins: $nick ( $+ $address $+ )
  dns $nick
}

on *:DNS:msg #chanY $dns(0).nick $+ 's ip: $dns(0).ip

If it comes back blank, it failed to resolve.

LonDart