I don't know what the "Right" way to do it is... but when I used to make images, I used to log in with a local account (not administrator) and make any changes that I wanted. Then reboot, and log in as Administrator. Go to System Properties\Advanced\Profiles and copy the profile I made the changes to, to "C:\Documents and Settings\Default User", and then change the permissions to "Everyone". Then from that point forward all new accounts are created with desktop, screensaver, power options, etc that you defined in that desktop. Seems to me this was suggested at http://www.appdeploy.com/, but I can't be sure. You might check that site out.
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(... better days ahead)