You can't do that with ColdFusion alone, and as it's a security issue, you'd need either a Java applet or ActiveX control to get this information. You can't just grab anything you want to off the user's machine; there's a privacy issue involved and they'd have to accept a control program that would be downloaded to their machine to perform this functionality; think of all the extra spam this would create, if a web site could just grab email addresses at will from each machine connected.
-Tek