I have an extranet domain (DomainA) and a corporate domain (DomainB). I have a
MOSS 2007 environment installed in DomainA with a trust to DomainB. I have
setup AD groups in both DomainA and DomainB and assigned users to those groups.
I then assigned the AD groups from both DomainA and DomainB to my MOSS
environment in DomainA. MOSS sees the groups and is authenticating the users in
the groups appropriately.

The users in DomainA with the MOSS install have been imported and if I create an
alert for one of those users, MOSS picks up the email address for the user. The
problem is that the users in DomainB cannot create alerts because MOSS doesn't
have their email address. Is there a way to allow the user to enter their own
email address when creating an alert? I thought I could do this in WSS but MOSS
doesn't seem to work the same way.

If not, what is the best approach for importing users from a trusted domain?

I have looked at the Active Directory Resource and LDAP in the SSP for the
Profile import but I am completely confused as to how to set that up with a
trusted domain.