I set up some relatives with a Linksys cable modem router on their
Comcast connection. It is the WRT54G2 V1.5.
As soon as we connect the computer directly to the cable modem the speed
increases by a hell of alot.
I have WPA encryption enabled with a long password; a few sports figures
names and a massive number - 20 characters and impossible to guess; so I
don't see how anyone can be using it illegally.

Could the router be bad?