Redmine

Hi,
i'm currently testing redmine and it's very interesting.
I've two questions:
We have a windows domain with AD (i don't manage).
Can i use ldap to authenticate with the AD ? And can i use concurrently local created users ?

What is about regular updates and maintenance ? I'd like to use redmine with access from the internet. So security is is very important for me. Are there regular updates/security patches ? How are they provided (rpm,deb,tgz,sh) ?
Is there a long term release which is maintained for a longer period ?

Thanks for any answer.

Bernd