1.Download Nvidia Inspector 1.93 and open profile settings.
2.Open the NV profile and remove falloutnv.exe from the profile
3.Open the Fallout 3 profile and add falloutnv.exe to it. (Be sure AO is enabled in the FO3 profile.)
That should work, though 'I' did it the hard way

It works great and AO looks lovely (except for grass), though there is a small fps hit. (using 260.93)
Cheers!