RE: [Zope] Question about logins?

I have a situation where I need to be able to programmatically add users to the ACL_Users on three different Zope machines running three different apps.

Hmmm, Well that's a toughy. I'd explore xml-rpc. Then you could just hit a method on the other 2 machines. Seems to me you may be going around this backwards though. Perhaps you should explore an SQL based user management situation. Then you would only have to update your DB once and all 3 zopes could query the DB for user authentication. Just some free advice.