Is there an active directory attribute that shows a users domainusername ?

If you are looking to get domain\saMAccountName in a variable, you may be able to use the Directory attribute msDS-PrincipalName.

This attribute is available if you have a Parent / Child domain structure.

The variable usage in webNetwork would be the following:

@@attr:msDS-PrincipalName@@

The information from Microsoft on this :

http://msdn.microsoft.com/en-s/library/cc221208.aspx