ATI - Invalid Display Adapter Error - Adapter Disabled - Incompatible Driver (4870 X2)

I ran into quite a few issues trying to install a new video card today, the ATI Radeon 4870 X2 by Sapphire on Vista Ultimate.

After pulling the previous Nvidia 7950 GT from the system and barely fitting in the  monstruous 4870 X2, I booted into Windows and proceeded to install the latest drivers 8.10. Prompted to reboot, I did and then disaster; Vista would disable at least one of the adapter saying something along the lines that the driver is not compatible with the VGA adapter installed. Something that made absolutely no sense.

I did try uninstalling and reinstalling many times, while also making sure there are no more Nvidia drivers and files left. Not much luck there for me.

Here's what worked after all:

- Uninstall any and all display adapter and ATI software from the Control  Panel/Remove Programs, including the ATI Catalyst Install Manager. When finished and prompted to reboot, don't.

Download and install Driver Sweeper from Guru3D. It's a free and clean piece of software.

Analyze and clean for ATI and Nvidia display drivers using Driver Sweeper. If you get errors just close the program and reopen and do one at a time: ATI - analyse and clean, then Nvidia.

When done, reboot. When computer restarts, hit F8 to be prompted with the Safe Mode startup screen.

Disclaimer: The following stepsmay involve making changes to the registry either by using automatic software or manually removing files. Backup your registry first. There are many guides who show how to do that. I take no responsibility for anything that may happen by following these steps. They just worked for me.

Now I don't know if it's like that on all computers, but I had the option of enabling Low-Resolution (640x480 mode). I chose that option to boot. Once in Windows, I went to Device Manager and uninstalled whatever was under Display Adapters. Then I ran Driver Sweeper again and cleaned as much as possible for ATI and Nvidia files. If Driver Sweeper fails to clean some registry files, just check the location, run regedit yourself and delete these files manually.

Reboot.  When back in normal Windows, I downloaded and installed the previous version of the drivers, 8.9 as I had read that some had success with that. After installing things seemed back to normal. I rebooted and then also obtained the latest hotfix for Far Cry 2 from ATI, which is a slightly updated version of the 8.10 drivers, somewhat newer. 

That's it. Hope it helps somehow.