automatically update a Web.config file to be prepped for IIS7 instead of IIS6

C:\Windows\System32\inetsrv\Appcmd migrate config C:\Whatever\MyApp\

...is a command line command that should update the Web.config in the second directory to jive with IIS7 per this. All of the magic for IIS6 in the </system.web> tag should be crawled and rewritten as magic for IIS7 in the </system.webServer> tag. I don't think it will work if you do not have IIS7 installed.