Thanks for the ideas. I did get it to go to Aero.
I had IE10 showing the Seven Forums in the background while the theme changed from classic to Aero. Making the switch seems to have fixed things... but I know that I tried that before.
I've already set it back to classic, saved the theme and deleted the old one. The Seven Forums' pages (and other pages) look normal. I'll test to see if it holds after a reboot... but I'll have to wait until Windows Update completes the .NET 4.5 patches.
It took a very long time to uninstall the 19 .NET updates and .NET4 itself. Maybe one of those uninstalls did something unexpected to the way the theme change acted this time. Dell's add-on for detecting the laptop's service tag claimed that the .NET 4 install was bad - hence the move to .NET 4.5.
Edit: IE10 looks fine - even after a reboot.
Edit2: Dells add-on works with .NET4.5
Thanks so much for your help. I probably would not have tried the theme change again. The user does not need any of the accessibility features. I just found references to that causing issues with webpage backgrounds.