Trillian Pro does a rather tricky thing with the Hotmail web site. If you're logged into MSN Instant Messenger, it can monitor your hotmail account and notify you of new messages. And when you click on a new message, it creates a little web page on your hard disk with the necessary Hotmail authentication information embedded and then opens that page in IE. That page opens and then "does the right thing" to connect to the hotmail site without asking you for a login. I'm not exactly sure how they go about doing this, but you might want to look into it, it might give some clues.