Although I am not an expert in .htaccess files, I have to say that what you are trying to do is mighty difficult.
I was thinking of creating a program that would check all passwords in the database and update them to the MD5 mechanism. The problem that we have though is that both crypt and md5 are hash and not encryption algorithms. The difference is that an encryption algorithm caters for storing information on how to decrypt the source, while the hash is not meant to be "reverse engineered" on purpose.
I really don't know the size of your site (users wise) but just a thought would be to tell everyone to change their passwords (and that would include only members that signed up before you changed to 6.1.1. This way the md5 mechanism will be invoked in the changebasic.php and all passwords would be in md5.
Sorry but that is as far as I could get with this....
Warm regards
Nikos
