Drupal Version 6 ?

Hi,
I’m migrating users from Drupal 6.38
In password.inc it searches for the 3 first letters of the hashed password.
The options are $S$, $H$ or $P$.
In any other case the login fails.

I have a hashed password that starts with “9a0”, and the plugin didn’t work.
However, when I changed the code of the plugin to simply compare the entered password after MD5, to the stored hashed password, it works.

What’s the difference between using the _password_crypt function, and just using the MD5 function?
the _password_crypt function demands that the 1st and 3rd chars are “$”.

Could it be that older drupal versions (6) use different MD5 encoding?
Is it safe to just compare passwords using PHP’s MD5 function?

Thanks and great plugin