The motherboard you currently have DOES NOT support PCI-e2.0... although the 9000 series will still work with your board as they are PCI-e1.1 backwards compatible
I agree. I currently own the P5N-E SLI. Great board but as said, only has the PCI-E 1.1. The card will work fine, but it may be slightly capped as far as performance. I remember Tom's has an article comparing the difference you'll see between PCI-E 2.0 and 1.1. I think at the time, there was only something like 2-5% difference in performance.
Still a great board. With the latest BIOS, it'll take the 8000 series dual-core Penryn's.