>can someone recommend a good FTP program for uploading and downloading files from the server?
CoreFTP-LE is a good free ftp program for windows. Also windows has one built into windows explorer. Open any windows explorer and type ftp://upload.comcast.net into the address bar and follow the prompts.
If you use the server space associated with your username on the web server to store files you will need to activate the web page feature in the 'my account' settings for the account. Any files uploaded by ftp will be marked public by default.
I think you can create (if it doesn't already exist) a folder called filelocker (or whatever name you want other than site) and make it private. Then put your files in there. Check that you can't get to them through a web browser.
Although it's there, I wouldn't trust it as my only backup. Comcast could remove the feature at any time.