My first sentence stated that PAE "is not supported on 64-bit operating systems" - I was merely trying to explain that while in both cases the same function is served, that of address extension, x64 does it natively and without "a separate PAE mode." This is an important comparison because it means that with either OS he will still need motherboard remapping support, but that the PAE switch is only required for the 32-bit OS.
In any case, I believe Vista 32-bit still limits you to 3.25GB at best regardless, in order to mitigate 32-bit signed driver errors from address extension (common with PAE), which are protected by DEP/NX, in addition to reserving the space for mainboard/video resources.