Cube and graficcard Geforce 2mx64MB

Hi! In my Cube originally is an ATI Rage Graficcard. In changed now to the Geforce 2mx64MB, but I can't use it under SuSe Linux (Kernel 2.4.12, KDE 2), the Monitor (Apple Studio Display 15") stays black. That means I had to go back to the ATI Rage. How can I configure both cards, that I can change? Thanks for your support! Peter, Berne, Switzerland