Domain shouldn't matter.
I'm going to make assumptions about your request.
a) you are authorized to connect as the intended user.
b) the rsh services are running on the target system and not disabled for security purposes.
c) you can already connect to the system, but want to do it non-interactively, ie: you don't want to have to enter a password.
let's say you are connecting as the user bakadm.
First, gather some info. Login to the AIX box from the w2k3 server as bakadm. Then type who am i , you should get somethin like:
bakadm pts/1 Feb 22 19:14 (w2k3-backupserver.my.domain.com)
take note of the info betweent the parans.
in the bakadm home dir on the aix server create a file called .rlogin and put the following line in it:
w2k3-backupserver.my.domain.com bakadm
then change the permissions on the file:
chmod 600 .rlogin
then go back the w2k3 box and:
rsh -l bakadm aix_servername date
and you should get back the date of the aix_server
then just sub date with the command you need to execute to start the backup:
rsh -l bakadm aix_servername "dsmc -i"
anyway, the details are up to you to provide.
-rs