From google searches I've determined that the ftp server you need to be uploading files to for AT&T is
ftp://upload.attbi.com - I think.
Your homepage will be
http://home.attbi.com/~username
You've probably seen this before but there may be some info at
http://help.broadband.att.com/index.jsp (and then go to "personal pages")
You'll need to find out your ftp username (which is usually some or all of the elements making up your email address) and then get an ftp client to connect to the server. Hope this helps...