I've written before about using Microsoft's IE Application
Compatibility
Images
with VirtualBox. These images provided a very convenient, and free, way
to setup testing environments in all versions of Internet Explorer.
The images, since they are free copies of Windows, expire after a time,
requiring you to download a new image. The latest images provided by
Redmond, require activation if you use VirtualBox, or probably any other
virtualization environment instead of VirtualPC, which is windows-only.
Whether or not this is intentional is hard to say, but I don't think
that it is.
If you have the old images, it seems like you can keep using them. The
only limitation I've run into is that the machine shuts down after an
hour. For web-development work, that's been sufficient time for me to
test and fix web broswer rendering bugs.
To keep up to date, you can follow this
thread
on virtualbox.org, or Pete Lepage's
blog, he's "Product Manager, Internet
Explorer, Developer Division." and is trying to track down a solution.