This will be somewhat long, but I hope it helps you...
Items in iweb that use ActiveX for sure:
Drop Shadows
Lines and Shapes
Navigation Bar
Reflections
Borders
Quicktime movies
and other items that might be "interactive"
My suggestion would be to disable all of the special features and slowly start adding them in one by one to test which use ActiveX. The above have all been tested and use ActiveX.
Note: If you publish your site on a CD or Flash Card, etc, and try to run it on a PC you will get an ActiveX popup. IE7 has an ActiveX popup if you run a website from the hard drive. One workaround is to publish your website online and test it in an IE7 machine. Another workaround is to use the web sharing (apache) service built into OS X on the same network as the PC. You can access the service from the sharing settings from your system preferences. Click web sharing to turn it on. Then publish your website into the library/webserver/documents folder. The address to your published site will be shown in the sharing settings when you click "web sharing"
Some workarounds:
Build your own navigation bar using hyperlink rollovers. These do not use ActiveX.
Do all of your drop shadows, reflections, borders, lines, shapes, etc with Adobe Photoshop or similar program. There is a workaround for importing quicktime movies; I have not attempted it but you can find it if you do a search.
Don't forget to update your iweb to the new version that was released on Jan 30th.
Good luck and I hope this helps.