Is true that the TredSoft Multiple IEs Installer doesn’t work at all on Windows Vista, but quoting the owner:
Since the preview releases of Windows Vista, I received hundreds of emails asking about the possibility of running Internet Explorer 6 under Windows Vista or complaining that my Multiple IE installer for the standalone versions of Internet Explorer does not work under Vista. This shows that some web developers consider Microsoft’s solution unreasonable while others are still unaware of it…
There is always a solution.
Check the full article, it will worth the time: Multiple IEs on Vista Article Link
After testing the option given from Microsoft and even the Tredsoft multiple IES solution, I was presented with IETester which works almost perfectly on Vista. You can test from IE 5.5 to 8. Great tool.