Simon, Yes. The Xeon 5500 series processors supports both registered (RDIMM) and unbuffered (UDIMM) DDR3 memory at speeds 800, 1066 and 1333
The E5504 will only support the 800MHz memory speed.
I found this information for you.
Intel 5500/5520 chipset series supports 3 DDR3 DIMM tyoes:
Only unbuffered ECC and Registered DiMMs are appropriate for servers and wrkstations due to error correcting capabilities.
Great, thanks a lot Chris!
Just to clear up a further thing I was unsure about, am I right in saying that the standard non-Xeon "Core i7 920" processor does NOT support ECC ?