I have uploaded v1.5.2, which has been tested on Vista using Outlook 2007, clean install.
The Create Rule... button will only work if you have an email selected, as it takes details from this email. I have changed this in the latest version such that if no email is selected, a blank Add Rule window is shown. If it is not possible to add a rule from the given location, a warning is given. I couldn't find anything wrong with this (i.e. it did work so long as a message was selected), but changed it for clarity/completeness.
A couple of minor bugs have been fixed.