Well...

First off, Word documents can contain two different kinds of things,
document *properties* and document *variables*. They aren't
interchangeable.

Custom document properties can be inserted in the File > Properties >
Custom tab. I have no idea why you can't get that to work, although
public computers can get screwed up in a million unimaginable ways.
The same properties can be created through VBA instead, using the
ActiveDocument.CustomDocumentProperties.Add method. To display the
value of a document property in the document (including its header),
insert a {DOCPROPERTY} field containing the property's name.

Document variables must be created by VBA code; there is no dialog for
them. To do this, you use the ActiveDocument.Variables.Add method. To
display them in the document, insert a {DOCVARIABLE} field containing
the variable's name.

[Hint: If you use the Add method to try to define a variable that
already exists, VBA throws an error. A better method is simply to
assign it a value, like ActiveDocument.Variables("foo").Value = "bar".
If the variable doesn't exist yet, this statement creates it; if it
does exist, the statement changes the value.]

I'm trying to understand what you're doing. Am I correct that your
AutoText entries contain both plain text and fields, and you want the
fields to display the user's input? In that case, yes, I think
document variables are appropriate. However, I think you should look
into userforms (see, for example,
http://www.word.mvps.org/FAQs/Userforms/CreateAUserForm.htm) instead
of individual input boxes. Once the userform has collected the user's
input, the code attached to the form can create the document
variables. There are advantages to this: the code can validate the
input (for example, to make sure the user hasn't left a required field
blank), and it's less annoying to fill out one form than to be
presented with a string of popups.

--
Regards,
Jay Freedman
Microsoft Word MVP         FAQ: http://word.mvps.org