ssh and keys

[m.roth2006 at rcn.com]

So, here's one for the assembled knowledge base here:
   if I use ssh-keygen to create a key pair, and put the public key on the remote box, so that I can ssh in without being prompted for a password, this leaves me confused about a couple of things:
   1) is the ssh key pair in parallel to the real password 
        for the account? That is, if I create a keypair and
        use either no passphrase, or some password other 
        than my actual password for the account, does ssh
        go *around* the standard authentication?
   2) since the remote box ages passwords, does PAM know
        that I'm using an ssh key pair, and age *them*,
        or do I merely have to change my real password in
        a timely manner, but don't have to regen a new
        ssh key pair?

Thanks in advance.

      mark