If you have the latest BIOS there should be no reason as to why it wont work in PCIE 1.1 mode - it just means that it wont run as fast as it should (you wouldnt notice the differerence anyway)
I think that the PCIE 2.0 just means that if you run 2 cards they both run at PCIE 16 speed rather than one at 16 and one at 8 as older boards do - check the Nvidea website and just double check that its backward compatible - I would be astonished if it wasn't
