xw8400 workstation re-build

ok, so I'm apparently being sent the motherboard, and both Xeon dual-core CPU's from a HP xw8400 workstation with twin Xeon 3.0Ghz dualies for a christmas present .

Found 4GB of APT FB DIMM 667Mhz 240 pin, double-banked, so it should be ok in the HP, they apparently hate quad-banked memory.

I really dont know that much about servers/workstations at all yet. and this will be my first attempts at learning the differences with a workstation-class machine.

my main goal is to get it put together and folding. I'll use my desktop for everything else. I intend for this machine to be a purpose built folder.

my main points of interest at the moment are:

-where can I find decent, and faily cheap heatsink/fan combo's for my CPU's?
-will using a standard PCI-E gtx 550 ti and a 750GB 7200rpm seagate barracuda SATA HD be fine with this machine?
-when installing all hardware are there any special differences that need to be adhered to for proper installion of said devices?
-What size of PSU will I be needing for something of this calibre?


This next question should be in the folding forum, but maybe auggie or someone will see this, but if I replace the Xeons with quad-core Xeons.. will that allow me to grab the 16-core work units from stanford with HT enabled?

Thanks for any input guys

 

10-minute editing rule, sorry for the double-post.

I forgot to ask, which OS would be most recommended for a workstation-class novice such as myself?