It's called soft-modding, it is mostly using different sorts of drivers to fool the card into giving the options and enhancements of Quadro cards.
I got it to work on my GeForce FX 5600, benchmarked it before and after using SPECviewperf. It ran at about 1fps before and about 6-8fps after the soft-mod.
I remember that is was a pain to find the drivers and took about an hour to install, also games performance went down. The performance isn't as good as a real dedicated quadro card but it will help.Here
's an article on Guru3D that explains how to do it.