Been toying around with some cheapo nVidia Geforce 310 cards. They’re something to toss in if you just need to output video, with a DisplayPort and VGA ports. It’s also slightly better than the GT210’s that the old Mac Pro models embarrassingly came with. It’s not noisy, but it’s not silent either. The non-standard mounting holes doesn’t make it easy for aftermarket cooling either!
After a bit of tinkering and some more searching, I managed to get dual display out of this thing using the following NVCAP:
VGA / DVI-I – BAAAAAAAAQAGAAAAAAAAAAAAAAA=
Here are a couple of other ones that may be of use depending on the configuration of your own card:
DVI-I / DVI-I - BAAAAAAAAwAMAAAAAAAABwAAAAA=
DVI-I / VGA - BAAAAAAAAwAEAAAAAAAABwAAAAA=
(Sourced from: http://www.insanelymac.com/forum/index.php?showtopic=205995)