I'd be willing to wager that the extra pins on a Xeon probably don't do very much (maybe some of them do). I'm sure somebody can dig out a PDF that says I'm wrong, but that's fine by me. Intel and AMD currently disable SMP functionality inside the core. It won't be enabled because they don't want it to be. There is no difference in functionality between the s939 A64 and the s940 Opteron or the Pentium4 and Xeon. There's a difference in price, though, and that's why they've locked out SMP. Imagine how much money they'd make if their consumer processors worked in SMP. Intel sells millions of Xeons, don't they? At about twice the price of a Pentium 4, that's a lot of butter on the bread.
Z