Well crap, no luck on FO3 working ... though I do see a ton of reports of failures, and Bethesda confirmed major issues that they will not fix.
Win7/64/Ultimate, UAC disabled, tried in XP and Vista compatability modes, tried setting affinity down to just 1 CPU (though this doesn't seem to stick between runs like compatability mode does), tried windowed and unwindowed. It wants to lock up when the vault opens -- though I skinned out of there after about 20 reloads. Now it locks up every time I load into the Megaton house. Morrowind overhaul 3.0 runs like a champ.
Maybe I'll see about dual booting XP. The world just won't be right if I don't finish this game. Should have bought it years ago, shame on me.