On the current Mac Pro Apple is using:
• an Intel X58 "Tylersburg" chipset (LGA 1366, "Socket B", QPI)
and either
• Xeon E/X55x0 series (dual CPU models) "Gainestown/Nehalem" CPUs
or
• a Xeon W35x0 series (single CPU models) "Gainestown/Nehalem" CPU
The CPUs and DDR3 DIMMs are installed on a custom daughterboard. They add wireless circuitry (Broadcom? Atheros?), one of several available GPUs, a SATA DVD±RW burner and a SATA HDD. It's all powered by a ~1500VA power supply.