FREE WINDOWS XP IMAGES FROM MICROSOFT WITH PRE INSTALLED IE6, IE7, IE8 BETA, ETC!!! it expires in sept 08 but they reckon theyll make new ones.
http://www.microsoft.com/downloads/details.aspx?FamilyId=21EABB90-958F-4B64-B5F1-73D0A413C8EF&displaylang=en
FREE VIRTUAL PC APPLICATION!!!!
http://www.microsoft.com/downloads/details.aspx?FamilyId=28C97D22-6EB8-4A09-A7F7-F6C7A1F000B5&displaylang=en
ITS AMAZING!!! WELL I HAVNT TRIED IT YET BUT WILL SOON.
and theres also this is development too - some sort of emulator app or something
http://www.my-debugbar.com/wiki/IETester/HomePage