Pls help regarding ICS

I have installed 6 computers network with one windows 2000 server and 5 windows 2000 pro machines.I have enabled Internet connection sharing on my server for the purpose of using internet for whole network. All the clients computers are doing well with internet.Suddenly my boss has asked me that you should only permit the company’s web site e.g. www.xyz.com. No any user can open any site instead www.xyx.com. I m using ICS so pls brothers pls guide me that how can i do this with ICS so that only www.xyz.com web site should open and no any other web site.