I have a wireless router and 2 computers. I want the two computers to be able to be on a network together to share data, but only one of them to be able to access the Internet. I want the other to be completely safe and protected from the Internet. (Please don't tell me to just install firewall software...) I thought that this is what DMZ was, but now I think I'm wrong. How can I achieve this?

Thanks in advance

BTW router is a DLink DIR-615, a laptop with WinXP Pro(can access internet), and computer with WinXP Pro(want to block from Internet, but not from LAN)