Unfortunately we still have to support IE6 these days.
For Windows 7 one of the best solutions was XP Mode
But this is not longer available in Windows 8.
I ended up installing just real Windows XP on VirtualBox. Needless to mention licensing issues 🙂
Also I was told about www.browserstack.com but this did not work properly with my site.
The good thing about this service is that they have tunneling and you can easily test local websites.
But this service is not free…