Samba has been integrated into the default desktop builds of OS X for a long time - I'm pretty sure it was there in OS X 10.3, I know it is there in OS X 10.5. The Leopard server admin tool allows you to enable it and do some configuration of the windows service - and the directory utility allows you to make the OS X server check Active Directory for authentication.

All the answers you seek should be documented here: http://docs.info.apple.com/article.html?path=ServerAdmin/10.5/en/c2fs12.html