To find which DreamHost server a particular domain is hosted on, in the panel go to Users -> Manage Users and look under the Machine column for the user that controls the domain.
Finding the email server is a little trickier. Go to Domains -> Manage Domains, click on the small [DNS] link for the domain then look at the MX records. There may be an easier way to find the email server being used, but I am not aware of it.
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