I am adding a third monitor to my home PC, and need a second video card. I currently have a GeForce 7800GT PCIe x16 card, and only a PCIe x1 slot available. Will it cause any problems to buy a newer x1 video card and run it side-by-side with the 7800GT? I'm not needing SLI or anything, just the additional video ports.
You can certainly do that, but I would recommend getting a newer graphics card that can simply run all 3 out of the box. Most newer AMD cards do this, and it's becoming more common on NVidia cards. Just shop around for a newer card in your projected price range and read a quick review to see if it supports what you're looking to do.