Help configuring LAN

Every once in a while a bunch of friends and I get together to play a PC LAN. It is a very simple set up. We have a 20 port switch and connect all PCs/Notebooks to the switch. I arbitrarily configure each computer with a local IP address on a nonroutable subnet, no DNS and an arbitrary default gateway (usually pointing towards the server, though this is not necessary as there is no routing, only switching). Here is the problem, I can get the vast majority of computers to connect without trouble (disable firewalls, shutdown anti-virus, apply static IP) with both Windows XP and Vista. However, there are two guys who come whose machines don't work. I have beaten my head against the walls for hours trying to figure out why. They can see the server, but they cannot connect, they just time out when trying to connect, which looks a lot like a firewall to me. I have looked over and over for firewalls, but they don't appear to be on. Additionally, one guy brought his notebook one time and it didn't work (Windows XP). Later on, he brought two computers, both of them possessed the SAME PROBLEM. Another guy is using Vista and he has the same problem.

By trade I am a Linux System Administrator and possess enough knowledge with Windows to get it working, usually.

Thank you for your time,
-sdls

Some windows FWs, even though made 'inactive', do not fully disengage from packet filtering (sorry, no I don't have a list ).

Some AV products have FW features (again, no list)

Vista has a Network Wizard for setup; try using it and be sure to elect Private Lan and not Public.

Thanks jobeard, I'll try that the next time I have access to the trouble computers.