So after spending the whole weekend and most of today fixing driver problems, I finally got everything to work (I hope). As always it is the nVidia drivers that screws everything up. I had to use Universal Extractor to get inside the 196.21 driver pack, so I could manually install the missing drivers for what Device Manager falsely believed was a coprocessor. It wasn't, what I got was a lot of extra system elements.
What is most annoying is that even if right now I feel like I am a real expert capable of fixing all kinds of driver related problems, I know that in a month or two, I will certainly have forgotten everything that i have learned the last few days, and then there will be a new screw-up.
If anyone here knows about nVidia drivers, please tell me why Windows Update says my Geforce driver is up to date, when there is a newer one on nVidias home page?
And don't tell me that I should never, ever install nVidia stuff on my computer, as someone kindly suggested some time ago - my rig is based on an ASUS motherboard, so there is no way I can get it to work without nVidia, afaik.