Move AD authentication services to OS X Server 10.3.9 Possible?

I'm afraid I'm no genius... actually, pretty much of a noob... and hybrid environment documentation all seems to focus on one idea: co-existance of an AD server and an OD server. I'm in a home network environment, running XP on my computers, relying on the AD controller (2003 Server) for resource authentication. While I've stuck to XP to use design software, all the other users have switched to OS X (some 10.3, some 10.4 users), and the 2003 is getting outdated, so we're getting rid of the 2003 box, and switching to a G4 running 10.3.9. My problem is, I'm not going to switch to OS X anytime soon... funding among other reasons, and still need the authentication services supplied by the AD server. Is there any way I can move this service? I couldn't care less about home directories, roaming profiles, etc. All I want is the authentication tools. Thanks for your help!