CMS / Blog with sub-domain

I am redesigning and updating my website and blog. I am moving off of the existing hosts and consolidating. So:

I want to have the www site and the blog site on different subdomains. For example:
http://www.foo.com currently resolves to corporate site. This is being moved to a new server with wordpress as a CMS.
blog.foo.com currently resolves to a completely different server/host/ etc. This is being moved to the same server as the www site with wordpress as the blog engine. DNS aside, do I need two instances of wordpress to host the blog and the CMS, since I want completely different landing pages based on the http://www.foo.com versus the blog.foo.com.

The server is linux, hosted at godaddy if that matters. The new test site is http://territoryplan.com
thanks!
Steve