Hallo Leutz,

ich gebe hier einfach mal folgende Problematik wieder, welche Jason Jones in seinem Blog beschreibt:
http://blog.msfirewall.org.uk/2008/07/problems-accessing-office-documents.html

Um festzustellen, ob es sich um ein Vista / Office Problem handelt, wurde diese Frage in einem geschlossenen Forum diskutiert und hier nun die Antwort vom Microsoft Forefront TMG Server Team (Gershon Levitz) (ich habe den Beitrag mal ohne Uebersetzung gelassen):

When a user has logged in to a published MOSS site and the user clicks on an Office document and persistent cookies have been configured in ISA, the user should not be prompted for their user name and password. However when running Vista the user will be prompted for their user name and password again.

Cause:

By default IE7 on Vista stores the persistent cookies in a protected store and that store is not available to other processes. If the user opens a second Word document they will not prompted for their password as Word now has a access to a persistent cookie it received when the first Word document was opened.  

Workaround:

Add the public MOSS  site to the Trusted sites list in IE (on the user’s computer) and the user should no longer be prompted for their password a second time.

Ergaenzung vom 13.01.2009. So richtig scheint das doch nicht zu funzen:
http://blogs.isaserver.org/shinder/2009/01/13/update-solution-to-vista-problem-accessing-office-documents-from-sharepoint-document-libraries-that-are-published-using-isa-server-2006/

Gruss Marc