I would uninstall 360 using the option to save all settings and click no to installing the free toolbar.
Then reboot and uninstall the grapic driver if you put it back on. You can leave the rest of the drivers.
re-install the chipset driver right over the top, reboot and reinstall the graphic driver.
Verify that Aero is working and set the screen resolution to what you like.
Personally I hate DEP but I would re-enable both hardware and windows DEP and make sure the system can go through a few reboots without any errors. Norton was not causing those errors in the first place regardless of what the error report was saying.
Then I would install 360 again and see what happens.
If you had everything working on the same system before with the same version of windows I see no reason why you should have any errors at this point unless you have some kind of graphic related program or tool that was not present on the old installation.
Best of luck,
Dave