Most likely it won't work. This depends on your configuration and your OS. I have seen dual monitors work with 2 PCI cards(same brand, same model) under Win98, and I think there is support for it in 2000. You MAY get a V5 PCI and a Geforce 2 MX PCI card working happily in one machine, because they are both PCI, but if you have a V5 already the MX would do you no good(especailly in gaming).
By the way, the dual card monitor system that i saw working was 2 V3 3000's.
zs