Yes Windows XP can support a unlimited number of Cores. It is that it can not support more than 1 physical CPU. It can have 4,000 cores on it as long as there is just 1 physical CPU it will still work.
Yeah all # of cores are fine, just one physical proc. Windows XP 64-bit ed though can support multiple procs. I don't know the limit off hand but I've built dozens of servers that had 2 procs and used that OS.
And Mak is good like that. He's beaten me to the punch lots of times just like that