Wordpress mu domain mapping

I was able to install wpmu onto DreamHost using the instructions (including having Support setup the Wildcard DNS) in the wiki http://wiki.dreamhost.com/index.php/WordPress_MU
I am able to create additional blogs that reside as a subdomain to the parent blog site.
My attempt to add domain mapping (using the WPMU Domain Mapping plugin) however, has not been successful and I’m hoping someone who has done this can answer a few questions.

Do I need to purchase a unique ip address? If so, would this ip address be for the Parent Blog Site only i,e, what do I tell support? (P.S. any discount codes for unique ips?)

The instructions state: "Make sure that you have created the domain to work without ‘www.’ on the domain management page in the panel."
I did this for the parent blog site, but do I also do this for the domains I want the subdomain.parentblogsite.com to map to?

When I tried this earlier I would add the parentsite.com’s ip address (the set of numbers returned by a ping) to the A record of the domain I wanted mapped to the subdomain.parentblogsite.com When then pulling up the url I got the error: error id: “bad_httpd_conf”, which turns out to be a DreamHost only error…

I’ve seen some references to installing wpmu that talk about having to modify the httpd config file. Others suggesting that if you have wildcard dns set up you don’t need to worry about it.

Thanks for your help. If I get this fully sussed I will attempt to add my experience to the wiki.

Apparently the trick is to use Mirror Subdomain, then you’ll get rid of the error id: “bad_httpd_conf” error (techie explanation: this means that the URL was not loaded by Apache as a ServerAlias)-