Support for the Expression Web platform is limited to ExWeb 2 and Vista. Neither ExWeb 3 or Windows 7 are officially supported. So for the problem on Win 7 I think an engineer is working to get you a license file to see if it helps you. As for not seeing the extension in your other os what is the version of ExWeb you are working with? If it is 1 or 2 then you should be able to confirm that the extension installed by going to the addons menu and viewing the listed add ons, you should see the CSS Sculptor.