Well, here are my 2 cents in the subject, mostly from personal experiance.
Lets step back in time to the good ole days of quadro. The only difference between a quadro and a geforce, was the two capacitors that enables certain graphic functions, as well work with the bios. The quadro 2, and hence, geforce 2, was the same way. The geforce 3, and quadro dcc were a little bit more different, but still the same principle.
All of the quadro, quadro 2, and suadro dcc have software 'hacks' that enabled the drivers to recognize them through the firmware of the board.
NOW, the newest quadro, quadro 4, takes on a whole new approach to the difference between a quadro and geforce. So, listen carefully. If you want, get a geforce 4, and do this
SoftQuadro4
Otherwise, get a quadro 4 and be happy with the real thing like I am.
Here is a good resource for this topic.
Forum on Highend3d.com
Hope this helps.
-Steve