what is the best practice for transition of domains?

brief outline of situation

old painful server hosts online catalogue on domain http://www.foo.com with urls such as http://www.foo.com/template.aspx?id=1234

linode currently hosts WP blog on a subdomain, blog.foo.com

now client wants to migrate home page onto WP but keep old catalogue running. My question: What is the smartest way to redefine the domain(s), such that http://www.foo.com points to the linode server (ideally a page within the existing WP install), whilst keeping the old catalogue visible.

My vague and useless thoughts are: I could define a new subdomain (catalogue.foo.com) and have that resolve to the old server, and make the www. point to the linode server. but then i'll need to work some magic to make the url of the WP page look like http://www.foo.com, instead of blog.foo.com/homepage.

thanks for any suggestions