The 32 bits isn't related to the Operating system, it's the amount of bits in the memory interface, and in the case of dual channel operation, since each channel is 32 bits and you have 2, you have 64bits of parallel bandwidth.

When manufacturers says your ram is 533 or 667 mhz, in reality, you'll only getting half the real speed. They list it as 533, because DDR operates on the rising and falling tides of the clock, essentially 2 operations per clock, so in reality, a 667mhz ram is only operating at 333 mhz, and thus only a processor with 1333 FSB (667x2) can take advantage of it.

Remember you have 3 frequencies here
1) Base frequency, being 200, 266, 333.
2) Effective Frequencies, being 400, 533, 667 (Usually the DDR rating)
3) Compensated FSB rating, being 800, 1066, 1333

Thus before you ask any question, which one is your 800 mhz ram rated in? the 2nd frequency or the 3rd?