user authentification under a special account

Can anybody answer me a question about user authentification and
application pool configuration under IIS 6.0?

What I want to do is to run an ASP-Script under IIS6.0. This script
should run under a special account (no IIS predefined account), because
this script should be able to work with Clear case library (CAL) over
OLE. I have the following configuration:

The default Web Site configuration is:

Directory Security: Enable anonymous access, user name and passwd set
to my "special (ClearCase) account".
Virtual Directory: Using of an Applycation pool is confiugred

The Application Pool is configured like that:

Properties->Identity (Application Pool Identity): Configurable
(username and passwd of my "special account").


This configuration works, I can interact with the Clear Case library,
but the remote user (AUTH_USER) is not set in the Server variable. If I
change the Application Pool configuration to:
Properties->Identity (Application Pool Identity): Predefined/Network
Service
The remote user is set in the Server variable, but this user (Network
Service) has not the rights to work with clear case. I must work with a
clear case user account and also want to identify the user. The user
should not type in his username and password.

I am not a expert in configuring the IIS, so any hint would be helpful
for me.

Thank you


Udo Schmitt