Custom Attribute Modifications for AD 2003/Exchange 2003 User Accounts

Good Afternoon,
      My company currently has 8 different domains that are geographically separate.  Currently, each one has access to our Global Address List & also a modified Address List for each domain.  We would like to make this a bit easier to automate, as our Address Lists are currently built of information that is manually put in.  Here is essentially what we would like to do for each domain:

1. For each exchange account, distribution list, custom recipient, etc.  We would like to change "Custom Attribute 1" to be named "Exchange Domain".
2. We would like to do an auto fill for each new user account created so that the "Exchange Domain" value is filled with appropriate domain.  I.E.  If I was in Domain A -  When a new account is created for me- the Custom Attribute "Exchange Domain" will fill in "Domain A".
3. We would then like to modify each of the address lists to only query for the information provided for "Exchange Domain".  

We only want accounts that are user mailboxes, distribution lists, contact, or custom recipients (i.e. Address List addition for an email address of someone not in our enterprise).

ALL HELP is appreciated.

Thanks
Bryan Beulin
ASC Resorts