You should be able to access HDR from the graphics options somewhere (I have the Xbox version). One person said that the setting for HDR wasn't saved for them when they disabled it in the options, and they had to edit the configuration xml file (this fixed a black screen problem in certain locations).
In XP the configuration file is in the folder below. It can be edited in Notepad, or any other text editor.
C:\Documents and Settings\ %username% \Local Settings\Application Data\Divinity 2\Profile
or in Vista / Win 7
C:\Users\ %username% \AppData\Local\Divinity 2\Profile
You may need to set Windows Explorer to show hidden files and folders.
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