Asus P5rd1-vm

I have this motherboard and i wanted to know if i could support a PCI video card along with my PCI-E X16 video card

Yes, it will support a pcie and a pci video card at the same time provided you have an adequate psu and enough memory to run drivers for both simultaneously. What you planning to use for monitors?

I have a XEROX monitor which is my digital port and a ENVISION which is my analog, I have a 680w PSU. connected to my PSU I have 1 CD drive, 1 DVD Drive, a 160gb HD, the motherboard, and a fan. I also have 1,256mb of RAM. Is that enough?

Easily. What resolution do you run on the second monitor? What else do you ahve on the PCI bus? The PCI bus lacks alot of bandwidth, so as long as its just a secondary display...say a monitor for you to keep up on IM's while playing WoW on the primary digital, you should be ok.