I have opened a Gaming center as my business and I am having a very serious
problem that I need to get fixed as soon as possible. I have 18 gaming
computers all hooked up into the same LAN. The LAN is connected to the
Internet through a Qwest Actiontec DSL modem .

The problem I am having is that in all the games I have (which I have listed
below) when ONE user requests a list of available game servers it hammers
the Internet connectivity of EVERYONE on the network. It does this with most
of the games I have.

So lets say I have 17 people playing a game on the internet. Person 18
decides to look for game servers using his pc for "Counter Strike". ALL the
other computers stop responding and get a "network connectivity" error
message pop-up. Once that 18th computer has download/refreshed is game
server list everything goes back to normal, until someone decides to lookup
game servers again.

All the PC's have non routable static IP addresses in the 192.168.0.x range.

Their gateway is 192.168.0.1 which is the actiontec DSL modem. The actiontec
modem has it's own static ip address that is a public address. The two
switches are connected to each other via a cat5 cable, and one of the
switches plugs into one of the Actiontec ethernet ports.

Games:
Warcraft 3
Battlefield 1942
Counter Strike
Day of Defeat

Here are the players:

Internet service = Qwest DSL 640k U/D
DSL Modem = Actiontec DSL Gateway Model: R1524SU (5 port switch built in)

(2) Switches Linksys Etherfast 4116 (16port 10/100)

(All pc's have the following specs)
Motherboard = Intel PESVL
Nic = Intel PRO/100 M Desktop Adapter
OS = XP Home
Mem = 256mb

Here is a sub note that I though was REALLY REALLY weird. I also have 2 XP
professional machines plugged into the actiontec. One of those machines acts
as a LAN game server. It also has Winamp running on it that I use as my
music jukebox to pipe music in the gaming center. Get this, when someone
refreshes/updates their game servers and it kills the connectivity on all
the machines like I explained before I also hear the music pause on the xp
professional box at the exact same time as all the computers get the
connectivity problem. The music resumes once the server list has been
updated. What?

Please help me figure this out!

Dude, that cheap DSL connection is way to much for all those clients to be using for gaming. The gaming itself might not be so bad, but the server download list is pretty heavy and will suckup that WAN connection till it's done.

You might have to throw bandwidth at it, but before you do that- read up on the configuration settings of each of the games and see if you can set them to keep a static list of servers, instead of pulling down a list each time. I've heard of Unreal Tournament having this option, I'm sure the other games have it too. There's no reason for each person to have to download the entire list of game servers each time they want to go looking for one; just make the games store static lists and I bet that will solve a lot of your problem. If someone wants to connect to their friends game server that isn't on the list, they can manually use the open location function. And maybe once a week or month you can download new lists yourself and install them so that they stay current.