If you want your credentials to pass throughout all your servers for PPS to work correctly, you really need to enable Kerbero's. I found a couple great articles that explain this and the process to do it. Enjoy... http://blogs.msdn.com/martinkearn/archive/2007/04/23/configuring-kerberos-for-sharepoint-2007-part-1-base-configuration-for-sharepoint.aspx
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