I agree that the Comcast page-building tool is a poor excuse for a tool. Notice that it is not supported or advertised. There are many reasons for that.
We strongly suggest that you use some other tool to build your pages. Upload them to upload.comcast.net using your Comcast ID without the @comcast.net.
The main page should be named index.html (or one of the other names that work - that one does). The server is case-sensitive so index.html is good but Index.html (with a capital I) is not. Do not use server-side scripting.
Upload all supporting files using whatever FTP facility is provided by the tool you are using or a third-party FTP program.
If you have a business, I strongly suggest you host your pages elsewhere. These may go away at any time.