PCI 2.0 vs PCI Express x 16

I searched the board for an answer to this question but came up with nothing. This answer will be obvious to many. Please excuse my ignorance.

I'm looking to upgrade my video card. My motherboard is an ASUS P5W DH Deluxe. It has two PCI Express x 16 video card slots.

I'm thinking about getting a video card that requires a PCI 2.0 slot. Not sure if it'll be ATI or Nvidia, Comparison shopping now. This is a Crossfire mobo so it'll have to be ATI if I want two video cards.

The question is, will a video card that needs a PCI Express 2.0 slot work my mobo that has PCI Express x 16 slots? For all I know these are exactly the same and I'm being confused by a term of art. Thanks for the help.

I have the same issue on my Dell XPS 420. So it sounds like PCI X 2.0 is backwards compatible with PCI X 1.0. Tehn I'm assuming it's also true that any card I get, even if 2.0 spec'd, will be limited to the 1.0 throughput? If that' tru then I'm probably better getting an older model card that's 1.0 spec'd? I have a new 30" 2560 x 1600 monitor I need to upgrade from my 78000 GTX for and I'm shopping now. Thanks!