As acid_kewpie already explained, there is no connection between a hostname and an IP address. The hostname is just the name that is given to the computer when Linux is installed, for example, the default hostname in Slackware is "darkstar".
I suspect that what you're really attempting to do is associate a URL (aka "website name" or "domain" such as www.[your_website].com
) with an IP addrress (eg, 188.8.131.523) and again as acid_kewpie explained, that's handled by DNS ("domain name server")
The following article may be of interest: http://www.howstuffworks.com/dns.htm/printable