Synchronize Passwords between NT and Linux?

[Mario Biron <Mario_Biron @ almerco . ca>]

It may seem a little off topic, but the reason I'm asking it here is
because I have a firewall and don't want to allow them to telnet thrue it
to change their password on the mail server (heck, I don't even want them
to have a login shell!).

Anyway, anyone knows about a product that could let my users change their
password only once on the NT server inside our firewall and that password
would be updated on my linux mail server outside the firewall? 

Tnx