As documented ni the SDK, there is a JavaScript command you can issue to get the list.
No, it only works on command-based items. What do you want to do that requires checked items?
How can you still be using Acrobat 4? Not only did we stop supporting it over a decade ago(!!) but it was never supported on Windows XP. Are you still using Windows 3.1?
Acrobat 9, is also no longer supported – those more recently .