have you tried running the browser in safe mode? go start menu > accessories > system tools > internet explorer (no addons)

I would be prepared to bet my lunch that this particular 'Windows Explorer Not Repsponding error' was due to the Security software. What type are you using?

What happens is when applications are opened or you do something like open up another partition the Security software does something obnoxious and the OS can't complete the request in good time. In fact MS's recently released free security software was doing it to three PC's in our firm. Other culprits are Kaspersky, Norton, McAfee, Antivir...that I know of anyway. The Java implementation on Facebook's photo uploader also causes some of these AV/Security programs to go bananas too.