Quality of net connection and quantity of net connection mean a lot for game hosting. My friend hosts his CS server of a business DSL line and it doesn't lag and is very playable across 20 people.
Counter-Strike, in general, needs about 4-5k/person to be a smooth gaming experience. So, with 768kb up, you have roughly 76k up. Doing some some simple math, I imagine you could get about 16 people smoothly on your line, but about 18 would be pushing it. Another important factor for hosting the server is CPU power. If you intend to run adminmod, HLGuard, etc, you need some juice under the hood for 16+ people (1.0ghz+ is sweet).
vash