SQL query to populate column with last linked number from table

I have a question about finding what amounts to the "head" of a "linked list" and using this to populate a column in a query.  More specifically, I have a table which has two columns of numbers... a child column and a parent column like this:

Table: ParentChild
Child        Parent
1000        500
1001        500
1002        501
1003        1001
etc

I would like to create a query that will list numbers in one column and list the ultimate parent in another column.  To make it more interesting, if a number has no parent, I want it to list itself.  So, in this example, I might have the following results:

Query: NumberParent
Number     Parent
500            500         <== note that 500 is not listed as a child
501            501
1000          500
1001          500
1002          501
1003          500            <== note it took the grandparent
2000          2000          <== note that 2000 is not in the ParentChild table at all
etc

Is this possible to do in a SQL Query in Access?  I am using Access 2000.   I'm doing it now by exporting the ParentChild data into excel, doing what I need done there and reimporting it, but it sure seems like I should be able to do this another way!

If it is not possible, is there another (better) way to do this in Access? I've not used modules or forms or reports, so don't know what is possible there.

Thanks in advance!
Steve