Send a non-html, one word subject line and one word message body from your Yahoo address to your Comcast address. Do the same from your Hotmail address. Do they arrive?

If you haven't already done so, check Comcast.net's FAQ on setting up an email account for Outlook 2003 here;

http://faq.comcast.net/faq/answer.jsp?name=17742&cat=Email&subcategory=Outlook

I hope this helps. Post back if you have any more problems.

Mark