Being dev makes me fixing bugs that I have introduced while writing the code. Because current project is web app it is obviously tested in multiple browsers (CSS and JavaScript). It is also tested in the worst browser (according to my humble opinion) ever created in history of a human kind by Microsoft itself, Internet Explorer 6.
Working on updated version of Windows XP means that your IE version is updated to at least version 7. A huge chunk of the world is still using IE 6. Question then: How do you get IE 6 after upgrading to IE 7. Or even better, how do you get both of them? I couldn’t believe answer is that simple 🙂
http://tredosoft.com/Multiple_IE
Nice little installer that installs all the versions of IE on your or your fiends Windows. All the versions down to IE 3.
Have fun with your development and testing.
Gregster
Greg Gigon's wEbLOG 
There are some rare situations in which Multiple IE’s IE6 will produce some errors that real IE 6 does not, particularly with javascript for some reason. I highly recommend this post: http://blogs.msdn.com/ie/archive/2006/11/30/ie6-and-ie7-running-on-a-single-machine.aspx
Hi Keith
Thanks for this link. Good read BTW.
I was googling for solution and as one of them Multiple IE software came up, that seeme fairly reasonable.
Having some discussion with QA guys at work I was told same thing. It is not 100% reliable and those instalations are not totaly behaving like standalone IEs.
Take care, Greg