In addition to using the EDAC codes, you can use the CLI only HP utilities to determine this while the machine is online. The cli versions are far more lightweight than the web based ones and do not require you to open ports or have a daemon constantly running.
hpasmcli will give you the cartridge and module #'s of the failed modules. A little quicker than analyzing EDAC.
Example:
hpasmcli -s "show dimm"
DIMM Configuration
------------------
Cartridge #: 0
Module #: 1
Present: Yes
Form Factor: 9h
Memory Type: 13h
Size: 1024 MB
Speed: 667 MHz
Status: Ok
Cartridge #: 0
Module #: 2
Present: Yes
Form Factor: 9h
Memory Type: 13h
Size: 1024 MB
Speed: 667 MHz
Status: Ok
Cartridge #: 0
Module #: 3
Present: Yes
Form Factor: 9h
Memory Type: 13h
Size: 1024 MB
Speed: 667 MHz
Status: Ok
Cartridge #: 0
Module #: 4
Present: Yes
Form Factor: 9h
Memory Type: 13h
Size: 1024 MB
Speed: 667 MHz
Status: Ok
Status will change for failed modules.
As stuff is stored into, left, and eventually pulled out of RAM, some corruption naturally occurs (theories vary, but the one with the most weight right now is EMI from the computer itself). ECC is a feature of RAM and motherboards that allows detection and correction of this corruption.
The corruption is usually pretty minor (ECC can usually detect and fix 1-2 bits per 64 bit "word" - and that's waaaaay beyond the typical error rates), but increases in frequency with the density of the RAM. Your average workstation/PC will never notice it. On a server where you're running high density RAM 24/7 in a high-demand environment serving critical services, you take every step you possibly can to prevent stuff from breaking.
Also note that ECC RAM must be supported by your motherboard, and the average workstation/PC does not support it.
ECC RAM is more expensive than non-ECC, is much more sensitive to clock speeds, and can incur a small (1-2%) performance hit. If it helps, an analogy that works is RAM to RAID controllers. On your PC, that hardware-assisted software RAID built into your chipset is great protection against single disk failures. On a server, that would never be enough. You need high-end, battery-backed fully hardware RAID with onboard RAM to ensure that you don't lose data due to a power outage, disk failure, or whatever.
So no, you don't really need ECC RAM in your workstation. The benefit simply will not justify the price.
Best Answer
I know that the opposite is usually true, as I installed HP ram in a DELL just the other day (It was just normal ECC though, not ChipKill/ChipSpare).
However, because that RAM has chipkill, it will only work in motherboards that support ChipKill (the same as regular ECC DIMMs can only work in motherboards that support ECC). I know that there are some Tyan motherboards out there that support Chipkill, not sure about other brands.