@OP
Although some gaming cards work with NX, they are not supported and, even worse, the X700 is getting fairly old by computing standards. As for installing the driver I would either log in as administrator or at least right click the install file and select run as administrator.
FYI-
I have seen a test rig with a single GeForce GTX680 run nx85 just fine. The GTX680 is a current high end gaming card. It performed better than our mid-range workstation cards by far but we didn't have an opportunity to test against a high end workstation card. On the sim/gaming side we got really high frame rates at high settings but were able to drag it down a bit when we ran ultra settings with a popular flight sim. Our next test will be to run two GTX680's in a SLI configuration and possibly test a GeForce Titan if we can get our hands on one.
NX85