sadly it won't support pcie 1.0 or pcie 1.0a. a pcie 2.1 card would require newer chipset after g31/q965 and require pcie 1.1(at least) to run pcie 2.1 card. even so it is still having issue with some after market card and some certain amd model like 5670/5570. so called the backward compatibility is only applies to reference model in most case(nvidia) or limited to some model(amd).
keep in mind these chipset under the list do not suppose pcie 2.1 despite pcie has backward compatibility. these chipset will not support pcie 2.1
nforce 4
nforce 5
p4m900/800
661fx
p865
915 all series
925x
945 all series(some card may work but not all)
ati rd580/rd600/rs600 or previous series
nforce 610i/610a/630/650
amd 690x and previous series