You can certainly network computers on a cable connection -- you're sharing the same connection with other people anyway -- but the cable companies typically consider it illegal, or used to.
If you do switch to cable, be certain you install a firewall program, F/N, but then you'll have the regular experience of having to reboot and reset your modem parameters every time AT&T goes down, which is frequently. Nobody will tell you this, by the way, until you have spent hours trying to figure out what is wrong.