Well its simple really.
Here's the thing.
I have found, that with Windows 2000 (which XP is based on to a great extent), driver's that are "uninstalled" leave profile remnants -
So you uninstall graphics card X and acutally physically remove the card from your system (so that windoze doesnt pop up next boot for a re-install), and go look in the driver section - and its not there.
But windows 2000 has this option you can select in the add/remove driver dialoge named "show hidden devices" - when selected, you acutally see a (faded) entry of the card you just "uninstalled".
Now in most cases (at least, from my experience) the actual driver files (eg - .sys/ .inf ) files would have been removed, but the mere fact that windoze remembers this device, and can show some details about it, means that it hasnt totally discarded every bit of data/configurations surrounding it!
All that, is held in the registry, JUST THE SAME, even though you "uninstalled".
In my experience, that data can be unhelpfull when it comes to troubleshooting drivers.
These profiles that are held back silently are located in your registry just the same.
Now, while I have no occular or otherwise proof of this - a strong hunch tells me that the very same thing is true for winXP - with the execption that XP DOESNT have the option "display hidden drivers". (most likely due to them wanting XP to be less technical in certain regards)
I have this hunch because of similiarities in the problems I would have with drivers (seemingly caused by these remnant profiles in Windows 2000) - these problems (which I also stumbled upon in XP, were also resolved by treating them as I would the whole shaded profile feature of w2k - if you get me.
so I'm pretty sure its a "feature" Xp has.
Thats why I reccomended you be as thorough as possible.. and use a registry cleaner.
With winXp (if you're using it) just do what I reccomended on a surface level.
After deinstalling the first time, boot to safe mode and search your hardisk for "Nvidia" for example. (the folder is most commonly found in the root - i.e C:/nvidia)
Also, go to Run promt and type in regedit - and then when the program starts (be carefull here) pres F3 - and search for Nvidia, or anything like that.
Then procede to reboot/ (work from safe mode if you can) and do the reg-clean with REgistry mechanic, (which you would have installed prior to the beginning of your work.
just follow the other steps