Since almost all instant messaging clients are connected to some sort of web mail service (i.e. Yahoo!, Hotmail, AOL) shouldn't you be able to send a quick email using the very same IM client without opening a browser window? My Trillian IM client tells me when I have received mail from any of these services but I have to open a browser window to reply to the aforementioned mail. Feel free to build this and let me know when you are done. Thanks!