Hey Daveyx1,
Have you checked all the software updates and installed all of the available ones? especially the EFI firmware? Check the EFI firmware version on your system and verify that is the latest from this link. http://support.apple.com/kb/HT1237.
If the version is not right you need to install the software updates and restart the Mac. After installing the firmware updates install the Boot Camp drivers again.
Also I know that you had tried most of the possible stuffs to get the issue resolved. However if you haven't tried that please try this.
1. Boot to Windows in Boot Camp
2. Right click on My Computer and select Manage
3. Check the display drivers installed
4. Right click on that and choose to update driver
5. When the wizard comes up let it search for the drivers first
6. If it is not finding the appropriate drivers repeat the steps and choose to install from the disk
7. Insert the Boot Camp driver disk (i.e. Mac OS X install disk) and try to update the driver.
This should update the drivers for the graphic card and the issue may be resolved. If the issue persists, please run an AHT as there may be an issue with either the Boot Camp drivers in the DVD or the Card itself.
You will need to contact the Apple store for a different disk and try installing the Boot Camp drivers or analyzing the Graphic card issues.
Hope this helps you......
Regards !!!!