I have found that periodically the Download Manager window in IE 5.1 just appears as white space without any scroll bars, title bar - nothing. I tried trashing the prefs but to no avail. I then discovered in my Explorer prefs folder (Users -> username -> Library -> Preferences -> Explorer) a file called Downloads.html. I trashed that and all was back to normal. It does still keep happening, but at least I know how to get it back again.