Proftpd Active Directory Authentication

i used the tutorial virtual-hosting-with-proftpd-and-mysql-ubuntu-8.04 by falko to setup my ftp server. however i have about 60 users in my windows active directory domain that wants to user proftpd. is there a way to have proftpd authenticate the windows active directory user accounts instead of manually adding them to proftpd??

thanks for your responses