Google lets you narrow your search down to within a specific website, or to within a specific Top Level Domain (TLD), for example .gov.

You can do this by using the site: command in your search, for example:

• java site:sun.com - searches for “java” on sites with the domain name sun.com (this includes subdomains, like java.sun.com)
• java site:java.sun.com - more specific; searches for “java” on sites with the domain name java.sun.com.
• copyright site:gov - searches all US government sites (domain names ending in .gov) for the term “copyright”.