There are many resources to learn about Colocation web hosting.
I found this article very informative:
http://webhosting.devshed.com/c/a/Web-Hosting-FAQs/Colocation-Web-Hosting-FAQ/
Here's an overview of colocation hosting:
http://en.wikipedia.org/wiki/Colocation_centre and here's a place
you can buy some: http://www.netnation.com/ .