it depends on a lot of things, the main concern is ram and bandwith. CPU speed effects loading times mostly so if it is an intensive game you will need a good CPU. I would say on a machine if you want to run 2 games you need 2 processors 1 processor will not run a 2 dedicated servers of high capacity (15+ people). So I would say something around 1gHZ with about a gig of SDR PC133 or 768 PC2100 DDR, would make a very nice server to run 2 mid-range servers on about 20 people on a T1-T3 connection is good, otherwise you will get problems with packet loss from people farther away from the server.
 
Specifically what game are you trying to run on this machine??

ok, screw 2 processors and a gig of ram and screw 2 games at once.
 
We will be playing:
 
SOF2
Wolfenstein
Medal of Honor
Quake
Quake 3
Unreal Tournament
Unreal Tournament 2
Counterstrike
And what ever else floats our boat at the time.
 
My guess is that there will be about 15ish people on it max

well, if you won't get 2, then u can only play 1 game at once,likely without probs.
 
UT and Quake, u could prob get away with, older games, not such resources hogs.
 
SOF2 / MOH - u will need at least 2 cpu's for 15 people in each.or there will be serious lag
 
u could try a P4 2.4, and at least a 1g of mem, get a scsi HD, or the new western 15,000 36g rpm drives, and go from there.
 
Just MO.

Scrap the 2 game.... that was just a thought into the future...
I am looking for something we can make out of old parts....

Given that most dedicated servers don't load any of the games graphics code you really shouldn't need that much grunt at all. Anything around the minimum (and maybe a bit less depending on the game) requirements for the game should be able to handle it no problem.

From UnrealTournament\Help\ReadMe.htm :
 
Dedicated Network Servers - General performance guidelines
We find that a 400 MHz Pentium II can usually handle about 16 players with decent performance. The performance varies with level complexity and other machine speed factors, so your mileage may differ. Note that there is no absolute maximum player limit in the game; performance simply degrades as the number of players grows huge.
 
If you're running multiple levels simultaneously, Windows NT outperforms Windows 95 because of its superior multitasking and TCP/IP processing capabilities.
 
For best performance, we recommend having 64 megabytes of memory per running level. For example, for running 4 simultaneous levels, 256 megabytes is ideal.
 
The Unreal Tournament server uses up at least 28.8Kbits per second of outgoing bandwidth per player (on Internet), so if you run the server on a machine connected by a 28.8K modem, you'll only be able to support one client with decent performance. Dedicated servers that support many players generally require the outgoing bandwidth of a T1 line or better.

Excelent. Thanks!

for quake 3, u just need the minimum req. on the box

How do I go about running multiple game servers at once? I have never tried, but I'd like to know before I did it. Looking at running 10 or more servers at once.

simply install the games u want to run, and start them up.
 
UT u can run as a"dedicated" server and it sits in your system tray, other games u have to be IN the game to run the server so u would be using more system resources.
 
i know UT and Quake have "dedicated" servers u can run.

Can I run multiple servers of the same game?

Depends on the game. I know that games based upon the Quake 3 engine you can, you just need to specify different ports to use, of course.