If you set up the Linux box to act as a domain
controller (using Samba), the individual _users_ of
the Windows boxes will be authenticated. My real
question to you is what do you mean by "log in"? If
you mean "log in" as in use the Linux machine's apps
and such, you would need to do that thru LTSP and
forget about Windows. If you mean "log in" in the
manner of Windows Terminal Services, you'll have to do
some investigating. I don't believe
LTSP(http://www.ltsp.org) handles that kind of
functionality. Personal Note - Windows doesn't seem
to handle that kind fo functionality either but it
still tries.