After installing windows Vista i soon realised that there is no way to test my web sites on earlier versions of Internet Explorer 7. Unlike XP where i used a piece of software called 'multiple IE's' Vista didnt support this software.
The solution i have found to this is 'Virtual PC 2007" and an image called 'Internet Explorer 6 Application Compatibility VPC Image'
Virtual PC 2007 uses this image to create a windows XP evironment with IE6 installed. Pretty good solution i reckon.
Virtual PC 2007:
Download details: Virtual PC 2007
The XP SP2 IE6 image:
Download details: IE6 App Compat Test Image
Been using it all day to fix the bugs in my templates without any problems
that's what i always use, dno if it's available for Vista.... but it's available for _ALL_ O/s' that i know 
Linear Mode
