said by rody_44 :

you cant unless you are a tech and have all the security tools and such and are authorized by them to work on their main lines. if your ordering tv you could just order that and self install a modem later. but thats about it. FWIW, it costs comcast a lot more than 99.00 to have a tech come out and do it. im guessing with the bandwidth your using you dont have any time to watch the actual tv set