No Spamming: Do not link to your site and tell people to go there. Unless your link is pertinent to a discussion already in progress, any external link posted will be deleted and your account will be banned.
Probably they have 'just' banned your IP. Usually there is a way how to change your IP (unless you have a static or shared -private IP). New IP will 'unban' you
Well, that depends on comcast, whether they assign dynamic or static IPs. If they do static, then you could try to use one of Internets Anonymous Proxys to get to that site.