How can I install two video cards?

I have an AGP NVIDIA GeForce3 Ti 200 and a MATROX G450 Dual Head DVI PCI card. They were both in and working and then (months later) my monitor freaked out and I broke the install trying to update it. I know it works, I used them for months. How can I reinstall them? I always get one or the other, but never both.|||Go to their respective web sites and download the driver software.