MD5 in pg and php

Hi, I'm completely new to hashing, so please bear with me.

I want to store passwords in a pg db, MD5 seems like a good way to
enhance security (no more plaintext passwords over the line etc.) I
had a look at MD5, in PHP 4.3.4 there is a function md5() which seems
to work nicely:

echo md5('apple');

returns ae6d32585ecc4d33cb8cd68a047d8434 every time. Apart from the
PHP frontend, I also want to be able to use the same algorithm in
native pg. I found that postgresql-contrib-7.3.4 has a function
crypt() which I expected to work the same. However:

select crypt('apple', gen_salt('md5'));

gives values different from the PHP md5() function, and moreover,
they're different each time. Can anyone please tell me what I should
do to get the same result in native pg as in PHP?

Thanks!

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08:59-09:07
Fedora Core release 1 (Yarrow) Linux 2.4.22-1.2188.nptl