Httpd.conf and domain masking?

I am running Wordpress MU (multi-user) on my site which allows me to have multiple user-generated blogs.

Wordpress MU (with a plug-in) supports domain masking, so I can redirect a domain to

We have the Client domain properly set up using a CNAME, and the plug-in is properly configured in our Wordpress MU, but it appears that when the DNS request gets to our server, our server is throwing the user at an IP address and our Dreamhost VPS isn’t sending the DNS request to Wordpress MU.

I opened a ticket and was told that I might need to open up the “httpd.conf” file in order to configure this. I assume this is similar to htaccess or similar, but I’m not entirely clear how to access this file or what change I should make.

Any ideas?