Doing an upgrade from SQL 2000 Reporting Services to SQL 2005 Reporting Services in a scale-out deployment is not that tough task however while I was doing an upgrade in a Scale-Out deployment where the nodes are configured in a Network Load Balance farm I faced a problem where the setup generates an error in the middle of the reporting services 2005 installation and refused to continue, no worries; aborting the upgrade in this phase was not dangerous as the existing reporting services is not yet replaced... Digging more I found that the Default Web Site is bind to the NLB IP Address and in order for the setup to run without problems the Default Web Site IP Address should be set to "All Unassigned"  and not to the NLB IP, sounds logic the reporting services setup will try to read the site configuration by binding to the local server IP however the website is configured to listen only to the NLB IP address which will confuse the setup wizard, setting the IP Address to all unassigned will make the setup to read the site configuration with no problems.

Note: You can change it back again after the upgrade process