Missing *-mysql packages (apt)

Hi there.
(1) Recently installed Debian 4.0 off an official DVD (No 1). I am new to Debian and am very excited to have a "bash" at it.
I'm setting up Virtual Users and Domains with Postfix, Courier and MySQL (+ SMTP-AUTH, SpamAssassin, ClamAV) by following a tutorial on Howtoforge.com. The article does not allow for support.

(2) Problem - can't find 5 of the 18 vital packages mentioned in the howto:
postfix-mysql
libsasl2-modules-sql
libpam-mysql
courier-authmysql
courier-pop-ssl

(3) Pattern is obvious: mainly *-sql mising. Admittedly, the howto is based on Debian Sarge, but surely that wouldn't make such a difference (or would it)?
Seeing my bandwidth is a bit limited, I'm trying to sort this out rather than reinstall.

(4) My sources list looks like this (I have not changed it):
#
# deb cdrom:[Debian GNU/Linux 4.0 r0 _Etch_ - Official i386 DVD Binary-1 20070407-11:40]/ etch contrib main

deb cdrom:[Debian GNU/Linux 4.0 r0 _Etch_ - Official i386 DVD Binary-1 20070407-11:40]/ etch contrib main

# Line commented out by installer because it failed to verify:
deb http://security.debian.org/ etch/updates main contrib
# Line commented out by installer because it failed to verify:
deb-src http://security.debian.org/ etch/updates main contrib

(6) Set up services as described in howto. When I try "#telnet localhost 25, postfix naturally complains:
warning: process /usr/lib/postfix/proxymap pid 5652 exit status 1
Jun 10 23:17:51 localhost postfix/master[3311]:
warning: /usr/lib/postfix/proxymap: bad command startup -- throttling
Jun 10 23:18:51 localhost postfix/proxymap[5665]:
fatal: dict_open: unsupported dictionary type: mysql: Is the postfix-mysql package installed?

I can't find postfix-mysql to install it (or the others above). I've dredged the forums, but nothing.
Any ideas very welcome (apologies for long post).

TIA & regards,
ardugh