1. Yes.

2. This is confusing. Interop Dlls do not need registering with Regasm. So
that interop Dll is just a wrapper that lets your .NET app call the real COM
objects in shdocvw.dll. You run regasm on .NET assemblies that export their
own COM interfaces, not on interop Dlls that map .NET calls to COM calls.
Maybe that's what you've got, if so, just add the assembly to the setup in
some folder and set its Register property to vsdraCOM. Use tlbexp to
generate a type library and install that type library too, it will get the
right Register property automatically (vsdrfCOM IIRC). That combination will
do what regasm does, and the order won't matter. In general it doesn't make
any difference in which order things happen during an MSI install, and you
have no control over the order in the MSI install anyway.

3. I've not heard of a register dialog or register.exe, and I don't think
i've ever seen one either, so can't help you here,