IE7 is here and I thank any and all merciful deities who may have had a hand in that deal, but the suck that was IE6 has not gone away forever yet.
When you install IE7 it overwrites IE6. In the main, this is a good thing. For someone who needs to continue testing features in IE6, ees no so good.
Fortunately, others have pioneered the way and here is a very handy way to install multiple versions of IE right on back to IE 3.0, if you enjoy that sort of pain.