When I ordered Comcast, they threw in free installation, so the guy came out. He said that he had to install the software to set up my email and password for the account, but hinted that I could just uninstall it once he left, which I did.
He also had to call in to validate the modem as elektrolokomotive said.
However, I recently did a Verizon DSL install for someone, and the modem/router had a password that was not admin or anything I could figure out, and it wasn't listed in the book or on the confirmation paper the client got. The only way I could configure the router was to run their crappy installation CD, and then uninstall it when I was done.