While Core 2 Duo CPUs should start their migration to 45nm before the end of 2007, Xeon CPUs should only be following sometime in 2008.
This might upset some readers, but is hardly surprising. indeed intel has always been conservative with server CPUs. They are meant to operate in difficult conditions and with a high load, much more than other products. Here again, Intel prefers to migrate only once the 45nm dye process has been perfected.