I'm glad you submitted this because I thought it was only me at first.  The issue is definitely related to the proxy settings for me.  Initially, I had "automatically detect settings" activated, and the same failures were happening for me.  Once I turned off automatically detect and manually put in the proxy ip address, IE5.5 and IE6 started working.  So maybe you have automatically detect set and need to turn it off?  And if you're running behind a proxy, try to put that in manually.