IE Extension using VC++

Trying to develop an IE Toolbar extension using VC++ (ATL) to type in the username and password based on a custom event. Not sure how can the extension code listen for a custom event. 

I want to create and fire an event LaunchURL (something like below)and handle it in the extension code. 

var t = document.createEvent("Event");
t.initEvent("LaunchURL", true, true);
document.dispatchEvent(t);

Looking for some pointers to achieve this. Appreciate any help in this regard.

Thanks in advance,
Shan