I wish I could say for sure, but I don't have the ability to duplicate this in my lab. However, I believe rather than using Native Mode, you could use Mixed Mode. This would make it possible to add NT4 PDCs into the domain; Samba works well with WindowsNT PDCs.
Also, if you don't want to compromise that much, you can make sure that you are not running in Server 2003 mode, which is a super-charged Network 2003.
Finally, you may want to do a search for MKS AD4Unix, which is reported to help negotiate authentications between Samba and Active Directory.
There's a pretty good article on this at Security Focus.
Find information about Unix user groups in the UK.
This was first published in December 2004