It's not really clear indeed. I don't have Home myself, I only use Pro, which definitely makes use of multicore. Microsoft explicitly states that Pro handles up to 2 physical CPUs, each with multiple cores. So Pro should be able to fully use a dual Xeon quad-core (8 cores total) system.
XP Home is definitely single processor. But Microsoft did not state explicitly that Home can use multiple cores.
So it's probably best to go with XP Pro.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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