you cant purchase a MAC addy--its hard coded onto your NIC.
And about the cable companies, etc caring about networks--Cox Cable(here at least) even -sells- home networking kits and will set it all up for you to use with their net service=)
Nono, no. I know you can't buy MAC addresses. You could sign up *additional* MAC addresses (including your primary machine) to be able to DHCP an addy. So you could use a hub vs. a router.
AT&T BIS did the same thing (selling home networking kits). Most DSL companies don't seem to care. Comcast just seem determined to make an ass out of themselves.