IE8 mostly, but I also have Chrome working using the "C:\Users\mike\AppData\Local\Google\Chrome\Application\chrome.exe --in-process-plugins" target line fix. Kinda kludgy, but works great once it's opened.
I am having the same problem with a Rackspace hosted Exchange account. No matter how I try to set it up, I just get constant Username/Password dialogs. Can't proceed any further.