Utility to ID ECC memory?

[JPS]

Is there a quick utility or way to tell if the PC-66 DIMMS in a PC are ECC or not? I need to purchase some more DIMMs as an upgrade for a legacy Dell Optiplex GXa. I do not have physical access to the box, so I cannot look inside.

It currently has two 32mb PC-66 DIMMs in there right now. If they were ECC would it matter if I added a third non-ECC DIMM?

Thanks...