hmail 5.3.2 is beta. Nethertheless I installed it on a test machine. The change password plugin works for me. So it looks like some misconfiguration on your side.
There is no way I see to support others than md5 encryption. I want to have the plugin to be able running on a *NIX box. So I can't use hmail COM API which requires Windows OS.
Hum, same problem on hmailserver 5.3.1, so it's not an hmailserver issue...
I used squirrelmail before, and the password changer worked on it.
Other thing, there is a change in database when i use this plugin, but it only encrypt the old password in md5 and save it.
So the new password is never changed.
Maybe i use an old or a wrong version of this plugin...
Can you give me a link to your version ?
EDIT : oh, i don't see the post before me...so i will try the solution...
EDIT2 : are you interested by French localisation for this plugin and for setting plugin ?