[Dovecot] Dovecot LDA with Postfix - question?

[kbajwa]

Hello:

CentOS 5.2
Postfix 2.3.3 (part of CentOS install)
Dovecot 1.0.7 (part of CentOS install)
Dovecot 1.1.1 (Updated from www.atrpms.net)

Postfix & Dovecot are working fine. While reading "Dovecot LDA with Postfix"
document at http://wiki.dovecot.org/LDA/Postfix , I read the following
statement:

---------------------
Dovecot LDA with Postfix

System users

If you wish you use deliver for all system users on a single domain mail
host you can do it by editing mailbox_command parameter in

/etc/postfix/main.cf (postconf(5)):

mailbox_command = /usr/local/libexec/dovecot/deliver
#  or
mailbox_command = /usr/libexec/dovecot/deliver
#  or
mailbox_command = /usr/lib/dovecot/deliver
#  or wherever it was installed in your system.

Then run postfix reload and that is it. 
---------------------

Here is the problem; I do not find location of ".../dovecot/deliver"
anywhere on the system! 

1. Did I do any mistake during the Postfix and/or Dovecot
install/configuration?

2. Next, I plan to install "Dovecot-Sieve". Do I need the "mailbox_command"
for "Dovecot-Sieve" to work?

Kirti