how to know users ip if she/he still dont post any message

how to know users ip if she/he still dont post any message?
i have been schoked! yesterday i have only 25 users when i go here agin i habe 116 users already and i know thats some of them are spamers
how to know their ip"S but they hvent posted yet?
my moderators are asking me

You can check that from admin panel=>Misc=>Statistics=>Board statistics and look for the "Who is Online ?" section. There you will see a list of all the members(or Guests) that are online at the same moment you are online.

so how will i know if their the same person?

Well, you can't if they are not logged in, but it shouldn't matter that much if they don't post (and spam) anyway - you can always make your forums be invisible to guests by changing the settings in "Forum / Permissions".

okay thanks

Also, to stop spam, make it to where you the Admin has to approve the member.

This stopped all spam on my forum....