How to block Port 80

Hello,

So here's my current setup - I have a DLink WBR-2310 Wireless G router that is hardwired to my main desktop PC. I also use the router to access the internet on my laptop wirelessly.

We will soon be getting a 2nd desktop PC that we plan on hardwiring to the router too. Now, we want our sons to be able to play LAN games using the main desktop vs the new desktop. BUT we don't want the 2nd desktop to have access to the web.

Now unfortunately, it seems my router doesn't support the "block internet access only" option that some routers seem to support.

I asked around, and was told to block Port 80 (HTTP) for the second desktop. Now, how do I go about doing this? Can this be setup through the PC or do I need some special program? Preferably free.

Also, just in case it becomes too complicated, I just might decide to instead get a brand new router that supports blocking the net but keeping the local PC to PC connection. I've heard there are even some that will allow you to set the time to block the net? Is this true? Which routers do this?

Thanks!

EDIT: I am running XP Home SP2 on my main desktop PC. Vista HP on my laptop. And will be running Vista HP on the new PC. Thanks again!