Not sure. I made this theme/skin for an older version of Aston Shell. It may or may not work on the newer versions in Windows 7. I don't use Aston anymore so can't really check. :/
Should be a simple matter of double clicking the file in the archive you downloaded here. Just extract 'Classic Windows.atz' then double click that while Aston is running. Keep in mind though this was made for the older Aston. I don't know if it works on the newest version or not.
It is a theme for a program called Aston available at [link] so as long as Aston runs on Vista it should work fine since Aston replaces the Windows built in O.S. shell.
That is a question best asked on the Aston Shell software forums. I've only used Vista for about an hour. (It was 4 times slower than my XP install is.)
I have Vista Business that was pre-installed on my IBM Thinkpad, and I have tried Aston Shell software, but I did not like it much on Windows Vista... sorry