I don't think that's his issue as his fan's coming on full on the GTX 260, and the drivers for the GTX 460 are in "idiot res" (I assume this is 800x600 or something low like that). Sounds to me like a driver issue....
Wonder if the GTX 460 is installed in the slot where the GTX 260 was installed, without the driver first being uninstalled, and it's then picked up the GTX 260, just on a different PCI express lane, and not installed the GTX 460 driver.
Also, can you load up eVGA precision and see if you can see the different cards, and control them using that?