whois is a service available on the Internet to check for information about a web site. You can see the IP address of a web site and also the registrar and web site host. To check information about UK web site on .co.uk and .com web site go to this address - http://www.whois.co.uk/

example of a whois search,

Domain Name:
mtv.co.uk

Registrant:
MTVN Online L.P.

Registrant's Agent:
PSINet UK Ltd [Tag = PSINET]
URL: http://www.uk.psi.com

Relevant Dates:
Registered on: 24-Sep-1996
Renewal Date: 24-Sep-2006
Last updated: 24-Aug-2004

Registration Status:
Renewal request being processed.

Name servers listed in order:
mtvi-dns1.mtveurope.com 217.147.240.100
mtvi-dns2.mtveurope.com 217.147.240.101

WHOIS database last updated at 16:25:01 16-Sep-2004