custom properties in Word & Excel

I would like to automatically create custom document properties for both Excel and Word documents. Specifically, I would like the "Computer User's Name" added to the property field when the document is created. Is there anyway to do this automatically? Is there a system variable that I can automatically add to the value field in my custom property? I am trying to ensure that the user who gives me a document is really the user that created the document. Thanks.

Winzip doesn't like the archive - can't read it and tells me to redownload. Subsequent downloads don't work either. Is there another way to get it?
Thanks.