Migrating is still a good idea...

[Billy Crook]

Linux Weekly News just pointed people at an article Microsoft
published on Authenticating Linux Clients with Active Directory:
http://technet.microsoft.com/en-au/magazine/dd228986.aspx

Intentionally or not, it's a bit slanted to make Linux look like a
burdon.  Don't let it scare you.  The author clearly has some
questionable admin skills, but the explanations of how auth works, how
it evolved, and how to configure it is worth a read, and will probably
solve your problem.  I would strongly advise going the Kerberos+LDAP
approach because it will make the final switch a lot easier.