ACS connection and Windows authentication

Hi,

When starting ACS at the first time on a day, you get a signon popup to
authenticate once with the system that is configured for your sessions.
In the old client access I could set my connection properties to "Use
Windows username and password, no prompting".
I'm looking for the equivalent of this for ACS. We keep our windows and i
passwords the same. The i is at QPWDLVL 3.

When I look into the ACS connection properties I see the following
possibilities to set:

- Use shared credentials: Prompt for logon credentials that will be shared
by systems using this option. The credentials will be saved until the user
logs off.
- Use default user name to prompt once for each system: Prompt for logon
credentials once for each system. The credentials will be saved until the
user logs off.
- Prompt for user name and password every time: Prompt for logon
credentials every time a connection to the system is requested.
- Use Kerberos authentication; do not prompt: Logon credentials are the
current Kerberos credentials. The credentials must be trusted for
delegation.

None of these seem to apply to what I want to achieve. I do not have
knowledge of Kerberos, but I tried that option and it gave me:
MSGKRB001 - Kerberos error for system %1$s.
(Failure unspecified at GSS-API level (Mechanism level:
80090303=InitializeSecurityContext() len=16384 ctx=00000000
SEC_E_TARGET_UNKNOWN))

Do I need to configure something for Kerberos? Or am I totally on a wrong
path?

Thanks,
-Arco