Jesus if I had to reinstall windows after simply switching GFX cards I would be fuming. I don't even bother doing it when swapping mobos
I really don't get how people have problems every time, I've gone from ati, to nvidia and back with no issues, I've moved from sis mobo's, to intel, to nvidia without reinstalling without an issue.
The only time I usually need to reinstall windows is going to a new mobo with a different chipset when I'm using raid 0 as it normally won't work, but most of the time upgrading from say one intel chipset to a newer one is no issue, same if you go amd to amd or Nvidia to Nvidia, not always though.
But as said, stick the card in, it might cause a problem, but it might not, infact the majority of the time it won't, if it doesn't you've saved a LOT of effort reinstalling windows and every last app aswell as losing any small files you forgot to backup. If it doens't work, you've lost all of 5 minutes and gained some experience.
Personally I do generally do a basic uninstall of drivers, shut down, change cards, start up and install new drivers, though I have done it without uninstalling without issue also.
I don't really know why people think errant drivers are an issue, hard drives and OS's don't allocate sector 489 to gpu drivers, if you install Nvidia drivers and the OS fails to delete a file your new gpu drivers won't magically look up the wrong file, thats just not possible or how computers work. You install drivers and the driver will only ever call on files its installed.
Of course windows can be a little funny at times, any manor of things can go wrong with windows at any time, it can default back to older drivers, and be looking up data thats not there anymore occasionally, thats really got smeg all to do with the drivers themselves or any incompatibility.
Think about how many users without issue on XP/Win 7 use an ATI card and Nvidia for physx without issue, with both ati and nvidia drivers installed and working alongside each other
Likewise for decades people have used different branded gpu's to run extra monitors, sometimes with issues, often not.