One of the problems that many web designers face is the cross browsers compatibility issue between Internet Explorer and other browsers. When the design and alignment look fine in Firefox and Safari, it is quite likely that it will break in Internet Explorer. What makes it worst is that even within the various IE browsers, the code might not work as expected. What works in IE 7 doesn’t mean that it will work in IE 6. With the release of IE 8, it doesn’t seem to make the whole problem any easier (there is a feature in IE 8 that allows you to view sites in IE 7 mode, but it still doesn’t solve the fundamental problem) .
The second problem is that Microsoft doesn’t allow you to install several versions of IE in the same Windows (unless you hack it). If you install IE 7, it automatically replaces IE 6 and if you upgrade to IE 8, your IE 6 and 7 are gone. Even if you want to test your site in the various IE browsers, you won’t be able to do it (easily) within the same Windows.
If you are facing the above problems, then IETester could be the solution for you.