I just had a problem very similar to the one mentioned at: http://www.computer-aid.com.au/blog/2009/03/17/realtek-device-co-installer-is-invalid/
Once again, I was unable to uninstall a badly installed device driver (audio device driver).
Except this time, I had no prior disk image to revert to… it was a brand-new PC…
After quite some searching, I found an excellent solution at: http://thetechcorner.net/2008/01/11/windows-driver-uninstall-failed-to-uninstall-the-device-the-device-may-be-required-to-boot-up-the-computer/
This solution involves editing the windows registry, so be aware that incorrectly changing the registry could ruin your computer.
You go to device manager (via control panel -> administrative tools)
You look at the properties of the uninstallable device, in particular, the details tab… write down the weird string that looks something like: HDAUDIOFUNC_01&VEN_10EC&DEV_0888&SUBSYS_8086D608&REV_10004&3ACC46D&080201
You then start regedit, and go to: HKLMsystemCurrentControlSetEnum
under enum, you need to find a folder that matches part of the string you wrote down.
In this case, I found FUNC…
I then deleted the folder below FUNC…, but only the one that matched the rest of the string. Sometimes there is only 1 subfolder… but if there isn’t, then you must make sure you delete the correct one!
Once deleted, I restarted the PC, cancelled all the found new hardware prompts, and ran the installer from the motherboard drivers CD…
And this time it worked correctly 🙂