i dont really know anything about this kind of stuff, but isnt it quite easy just to recompile 32bit drivers/applications into 64bit?
Not all that easy.
First the driver code has to be 64-bit clean. That basically means no stupid assumptions about integer or pointer sizes. You'd be surprised how often minor programmer mistakes slip by and blow 64-bit cleanliness out of the water.
Then the driver code has to account for different PCI memory mapping. PCI devices and drivers have the luxury of full access to the 32-bit address space for bus-mastering et al (although some, like the SBLive!, impose their own artificial limits on PCI DMA addressing). When the addressable space expands to 64-bit quantities, that may become a problem. PCI devices may find themselves having to use a "DMA hole" under the 4GB range, like some ISA devices require under 16MB.
Third is possibly different overall conventions for things like SMP et al. Remember, NUMA is something that isn't yet supported in MSWindows. When it is, device drivers may have to adjust the way they work to get maximum mileage out of NUMA topology. Of course, this won't matter so much on uniprocessor systems.
Using the expanded register set is a rather distant fourth. It's not so important, except for bumping speed a bit. Also, updated compilers can theoretically take care of that without any fuss.
That being said, driver support isn't all that far behind. nVidia's already posting AMD64 drivers, at least for Linux. I imagine they'll have corresponding Win64 drivers ready to roll.
<i>I can love my fellow man...but I'm damned if I'll love yours.</i>
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