As far as I know, ATi and nVidia have always had clashing drivers when put onto the same system. When MaxPC built their nutty rig to have something like 3 or 5 monitors(before SLi) they used the same brand cards, citing issues originally trying to mix ATi and nVidia.
RMA the BFG, that's what a lifetime warrenty is for. I know it's going to take some time, but it's easier than sorting out driver issues.