Latency matters more than bandwidth when it comes to gaming. You need about 64-128kbits per client. You could host about 16 players in something like BF2, or CS:Source. You could probably get more, but remember if your server is public, it will constantly get pounded by ping requests and what not... That takes a huge toll in popular games.
With regular CS I was able to host 7 internet clients without lag, once the 8th person joined it tanked for everyone. This was about 6 years ago when I had 300kbits upstream.