A proper solution would depend on the need - ie do you need a solution which the user cannot revert, do you want this to restrict all access or as a portal/passthrough etc.
However without that info I'd say the easiest way to do what you requested is to change the proxy settings on the browser to point to the server:port of the website you have in mind.
For example if I set my firefox proxy to
www.google.com port 80, irrespective of what I type in the address bar I'd go to the google home page. But remember I can't even search for anything in google as the search results page would return me back to the home page.
in IE - go to tools - internet options - connection - LAN settings to modify the proxy. Not exactly sure about IE8 but must be something pretty similar.
HTH,
Arijit.
