I just posted some info on getting centos ds up and running with samba. this will allow you to simulate a windows pdc. with a few add ons you can really implement a complete solution for your environment.
I began with Fedora DS, but found that it wasnt as stable as i would have liked for a production environment. i will post my HowTo for Fedora setups anyway if anyone wants to give them a try.
Here is a link to the guide: CentOS Directory Server