My dad ended up buying some Motorola box off the internet.

The guide comes up with channels but it says "this channel should be available shortly"

I immediately thought that I need to register the box, so I call Comcast.

They say they can't register 3rd party boxes.

Is this true? or does anyone have a 3rd party box hooked up?

Damnit; I fucking hate Comcast.
I have a Tivo and getting it set up has been worse than having my teeth pulled. 2 "technicians" (or guys who don't know what the hell they're doing) have come to my place and a third is scheduled. I've even taken a trip to their service center at North& Elston, which reminds me of a prison. I'm sorry I can't help you much with your situation, but I just want to chime in and say Comcast blows huge balls.

My advice is to keep calling and each time you will talk to someone different. No one knows what the fuck is going on at Comcast, so chances are you'll get a representative that may help you register it. I bought my own internet modem and the only reason I have internet working is because customers register/activate the internet service themselves!

Good luck!
Keep the Better Business Bureau in mind if things start to get rough.

when you hooked up the box, do you get any channels?

I wanted to buy one off ebay, to have an extra one in the house. We already have a motorola box. would like it in each room.

I also recently got a Tivo and although it took a bit to get it working, the Comcast people that work their online chat service center are actually pretty good, they knew about the cable cards and how the account had to be setup. Finally was fixed when a really smart WOMAN technician actually had the dedication to go outside up on the pole and straighten out some signal strength issues. Neither of the stoner BestBuy type techs did that before, would just hook up the spectrum analyzer to the line and say good enough.