[Exim] Rebuilding Exim for SMTP authentication?

I need to set up SMTP authentication and realize that this means Exim has to
be rebuilt. I was planning on using cleartext authentication. I'm looking
for a list of steps I need to take in order to do this--preferably with
little downtime.

Also, I am very confused about <where> the following lines need to be put in
order to enable the SMTP authentication:

driver = plaintext
public_name = PLAIN
client_send =

Thanks,

Robert Sparks
Network Administrator
M3 Design, Inc.
rsparks@???
(512) 218-8858