Having issues with Comcast, they replaced old box (dct700) with what they're saying is the only one I can use, boxy silver thing that is ugly. I have asked for old one, they say I can't have an old one, stuck with the new ugly one. Anyone have experience with this? How do I find out if there are other options? If I buy one from eBay or somewhere else is that "allowed"?
Purchasing a set top box from E-Bay is iffy at best. You really don't have any idea if the box you're bidding on is actually a stolen or abandoned Comcast set top box. If it is, Comcast has every right to claim it as their property (and start charging you for it's usage).
Your best bet would be to talk to Comcast Technical Support and find out the exact specifications needed for owning your own set top box and then purchasing on from a reliable source. Comcast isn't likely to offer that information easily and you will likely have to press for that information.