Does Windows 7 support multiple simultaneous nVidia graphics cards with different drivers?

AFAIK, the new video driver architecture will not aid your situation. The official stance from Nvidia is no you can't mix cards, and experiences from other users is that your mileage may vary when you try to mix the pro and consumer cards.

Well i don't know if you are using QUADRO for a real issue however as you probably know, Quadro/GeForce family are closely related, price apart but Quadro drivers don't work on a GeForce BUT... there is a work around to enable 3d professional acceleration on GeForces (enabling Quadro drivers and detections) that theorically, could transform them into Quadros :

http://www.techarp.com/showarticle.aspx?artno=539&pgno=1

You can try if you like, personally i've never tried i'm from the AMD/ATI side of river.