Whois records will show you the name servers for a site, which will sometimes let you know something about the host. For example, the whois my Web site www.franklinveaux.com
shows you that the name servers are at hostgator.com, which lets you know that I'm hosting with Hostgator.
However, that won't always give you useful information about the Web host. For that, you need to do a lookup of the IP address for the site and then look in the ARIM or RIPE registries to see who owns that site. Or, better yet, use www.spamcop.net.
You'll need to sign up for a free account, but when you do it will show you the IP address and Web host for a domain name.