What is this???

I have an HP xw8400 workstation running Vista Ultimate 64bit, with 2 - 3.2Ghz Xeon CPU's. I am trying to determine exactly what these are, Dual cores, quad cores or what. CPUZ indicates these as Dempsey core Xeon DP5060procs, and it shows they have 2 cores and 4 threads, so I am assuming these are 2 dual cores, yet when I CTRL-ALT-DEL and go to the Performance tab, I see 8 performance meters as if it is registering 8 cores. I'm a little confused by this. Also, what sort of Overclocking headroom do these things have while using fully buffered memory which this unit requires???

If the proc is actually only a dual core, then how do I get it to only show the 4 physical cores in the Performance tab? And more importantly, if they are only really Dual Cores (Socket 771 Pentium D????) what upgrade options do I have? (Can I run 2 true Quad cores in this rig?)

I know HP has a wealth of documentation on these workstations, I'm just having trouble finding the specific info I'm looking for...Any help or knowledge would be appreciated...