I have the same issue exactly. Windows Vista Home Premium, 3.0GHZ, 2GB RAM, 512MB Video, Dell Dimension 8400. I have no clue why the screensaver won't kick in.
I just installed Windows Vista Ultimate and I noticed something odd. Even though the screensaver was set to start after 10 minutes it never started. I checked the power options. It was set to turn off display after 20 minutes, still nothing. I can't figure out why neither the screensaver or the power saving options are working. I had the same problem during the beta, but I just attributed it to a glitch in the beta stage. Does anyone know what could be wrong?

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