you ALWAYS had to change (clone) your MAC address, ever since the idea of splitting DSL/Cable to multiple computers... its just that some ISP didnt enforce it like ICANN said to.. but you see now we are running out of ip addresses (hence IPv6)..
see back in the day(couple years ago maybe 2000) ISPs just let modems come online (speaking cable) and assigned them unique IP's accordingly, but when some one is trouble shooting there inet, and plugs a modem into a new computer/NIC, the MAC address on that NIC creates a TOTALLY new/unique address on the internet. of course ISP buy IP's by the hundreds of thousands, but still there are so many available period on the the IPv4 schema.. 3.4 trillionish(or is it billion? i think its trillion) so that means that hundreds of "new" ip's could be takin daily.. see the problem with that now right? now when you sign up with ISPs, they request you have the modem pluged in and
turned on, some isps wont even get the data for you(MAC address), i have had one ISP run me through ipconfig and the whole nine just to make sure when i turn my comp on it knows who i am... therefore, if you dont have a MAC that is on "their network". then it no werkie werkie.
i hope this helps! ;p plus are you in florida, with comcast? cause my fren in jacksonville had very much the same probs, lol omg the same routers ROFL lol if my lil MAC clone no werkie, upgrade your firmware... and that should do it... we spent a couple days on his prob and found htat the firmware he got on his wireless linksys was the problem.. btw AIM is my THG login
holla if youget time on the weekend, im always on, leave me a msg and i WILL get back to you