Well, firstly, to get any kind of decent speed from the webserver, or any decent amount of concurrent connections to the game server, you're going to need one hell of an internet connection. Something with multiple Mb of upstream bandwidth, and preferably a connection on a very low contention ratio. A business grade SDSL line would probably be advisable if you want the gaming server to be usable at all for more than about 3 players.
Secondly, you can use as many hosts (game servers, webservers, mail servers, FTP servers, etc etc etc) on your connection as you like, but a standard ADSL+ line probably won't cut the mustard upstream bandwidth wise.