So if you wish to integrate with AD then you will have some work to do... AFAIK Samba4 interates with AD, but not Samba3 (at least not OOTB). I don't have any experience with this so can't help much but if you keep in mind that TKL v12.x is based on Debian Squeeze then you should be able to find plenty of info via google. Also you may be able to tap into the previous experience of other users here with a search (I searched "Samba AD" from the search box - top right of the page and got quite a few hits that may or may not be useful).

AFAIK any official additional Webmin modules (that exist) should also be available in the TKL repo (enabled by default). You can see all the Webmin modules available like this:

apt-cache search webmin

If you find instructions that work for you please post a link and/or document your steps and post back would be cool and I'm sure helpful to other users. If you get stuck please feel free to ask (although I'm not sure how helpful I'll be able to be...).