My forum is on a free host where the mail() function has been disabled. Some of my users lost there passwords and cannot receve them by email. I took a look in the db and saw that the pswrd was cripted.

what can i do ?

Actually, you can change these passwords only manually. Encode some phrase with md5() and update the database.

For example, this PHP code will echo the MD5 value for the password "aha":

<?php
echo md5('aha');
?>

Copy result to clipboard and update necessary record in database manually. That's all I can suggest for this case.