Depends on how many players you want to host, and how good you want their playing experiece to be.
The rule of thumb for the newer games...this rule came from
http://www.planetunrealtournament.com/theadminpage...is take your tested upload speeds, divide that by 28.8, that up to the nearest whole number, and that is the max amount of clients you can host before the next one that logs in starts eating into the bandwidth enough to introduce lag to everyone. So say your bandwidth tests at 384....you divide that by 28.8...the result rounds to 14. Say you only benchmark your upload as 110 or so...you could host about 4.
Now that rule of thumb was for Unreal Tournament...certainly a bigger engine that Quake3...but not by much. You could probably get away with hosting a couple of more than the above rule tells you. I find the two to play similar online for me.
Also something to consider is the quality of your ISP. At my house, my PPPoA aDSL line is 1.5/128...and upload test pretty close, like 120 or so. It's with a really good ISP. I can host only like 4 players til lag comes in....the 5th comes in and some lag comes in....but up to that point...they ping great. At the office, I have a 6 meg business class DSL line, with 384 up. But it's with the local phone company, not a good ISP. Download kicks butt, upload isn't bad either. But for gaming, I tried running a server from our server room...the server could host quite a few peeps...but the packet loss and lag was horrible. Even with only myself logged into the server...it sucked. Here was a business class DSL line with 4 times the bandwidth of mine at the house, but for gaming purposes...it sucked. And this was before my network at the office got really busy, with the Exchange mail server and networked anti-virus scanning going on.
Also, do the gaming world a favor....run a separate computer to run your dedicated server off of. There's nothing worse than newbie broadband-at-home admins who run a server on their only computer and play on it at the same time, enjoying a zero ping, sucking up all the computers resources for their own graphics and leaving nothing to help the performance of the poor suckers who log into this computer. It's OK to fire one off for a few hours now and then so two or three buddies can log in...but for a 24/7 server...bad.
If you can't build an NT box to co-locate at some ISP, (that's what I've done...
http://www.zombiebattalion.com is at my ISP, in their server room, which is fed by 4x OC-3 lines)...there are many game server hosting companies where you pay per month to have your own virtual server for many games. The price is dependent on how big you want your server to be (12 players, 24 players, 32, 64, etc). Usually little multi-proc Linux boxes that you share with other virtual servers, starting at 30 a month or so.
Check out
http://www.ilanstation.com
