Quote from gnome:
No, you cannot. Physically won't fit. You can plug an x1 into an x16 slot, however.
Quote from gnome:
The Nvidia choices are:
1. NVS 440 PCIEx16 and PCIEx1... a quad head.
2. NVS 290 x16 and x1
3. NVS 285 x16 and x1
4. NVS 280 PCI... this one supports 1600x1200 DVI max, while the others support up to 1920x1200 DVI max. If your monitors are the commonly available, 22", SXGA, you'll want to use the others and not the 280 PCI.
All of the x1 cards are in much shorter supply.