"afaik, Intel D cpu's require xp64 to take "full" advantage of the dual core. And with Vista on horizon, I've heard xp64 will have a short shelf life."
This is an erroneous statement. All current single core Pentium 4's and Dual cores support 64-bit except for the mobile Pentium-M and Core Duo/Solo lines. You do not need 64-bit windows to "take advantage" of them. The only reason to run xp-64 bit is if you are hitting some big memory walls. ie - when you require >4gb of system memory.
For example, the AMD64 chip has been on the market over two years now, the first year of which XP64 bit was not even a shipping product. As you probably know, AMD is doing very well with these chips.
Vista will be available in both 64 and 32 bit varieties, but it will all be "under the covers" so to speak. From winsupersite.com - "Unlike XP x64, you don't need to buy a x64-specific versions of Vista. Instead, all Windows Vista editions, except for Vista Starter, will come with both 32-bit (x86) and 64-bit (x64) versions in the box, on separate DVDs. This includes the Home Basic (and Home Basic N), Home Premium, Business (and Business N), Enterprise, and Ultimate editions of Windows Vista."
You are correct that the upcoming Vista release is no doubt inhibiting driver development for WindowsX64.