URL Masking

I have a website running and WordPress set up up on a different server, as we could not accommodate the install of WordPress DB within the primary web server.

I have added the Root Relative plugin and can get the articles and topics to behave as expected (e.g change the URL to http://www.mydomain.com/blog
but the theme as well as many of the plugins continue to resolve to the server that hosts WordPress.

Can any one assist in helping me understand how to set the blog mod rewrite up to have the URL resolve to http://www.mydomain.com/blog as opposed to its current internal designation as http://wordpressprd/blog?

Thanks
-Jim