<< in all seriousness, what kind of server are you plannning on running? from what i understand, dont most, if not all cable inet providers prohibit running servers? >>
Yep.. most have it in their TOS.. but you could always do a "Oh! I didn't know.. sorry officer. I'll play nice."
Anyway.. if you plan on hosting your own website and plan on getting a lot of traffic per day, the cable modem probably won't be sufficient because of your upload bandwidth (which is usually considerably lower than download bandwidth). It's usually something like 512k/s down; 128k/s up. Kinda the same thing with a game server -- you'll only be able to host an 6-10 player game. I ran one of my domains off my cable modem for half a year or so -- worked out alright, except for the fact my cable modem service wasn't all that reliable.
*Usually* you aren't going to get into too much trouble running services like that -- unless you're sucking up major bandwidth from your ISP or they're really anal about it (I think @home was in the past for a bit.. wouldn't even let people run telnet).
Good luck!