I have just upgraded from IE4 to IE5.5 by downloading from microsoft site. Instead of having microsoft install I selected to save to disk, I also chose to choose which componenets downloaded. Within that section I was given the option of keeping IE4 and having IE5.5 separate. Although I could not then use IE4 for email etc etc it could only be used for browsing. Dont know whether that info helps at all. I now have both versions so can easily view my web pages in both vaersions
While we're here, I'm wondering if it's really necessary to have several different versions of MSIE. A tool like Browserola can strip away tags that particular browsers don't understand, but are there any fundamental rendering differences between the different versions of MSIE? In other words, if a page looks good in MSIE 5, and doesn't have any tags that older versions won't understand, will it still look good in the older versions?