Split Application

I currently have an application that has "evolved" over a few years. Currently that application is a single exe with all forms, classes & modules in the one project. I need to develop a secondary application that uses alot of the forms and classes from the first application. What I want to do is to split the forms and classes from the first application that I want to use in the second application out into an activex dll that I can call form either application. Can anyone point me to any articles on this or pit falls I should look out for.

You can not directly pass a form from a dll, you'd have to pass it as the generic object and there can be trouble with that some people say. Nothing that can't be overcome of course.

Overall I would suggest taking a normal two or three tier approach and break out the object models (classes) to a dll and then have the applications contain just the user interface and call the objects from the dll. If you would rather share forms as well then I would set the forms up somewhat like Msgbox where the application doesn't directly access the form it just calls a function or what not in the dll (i.e ShowLogIn) and the dll handles showing the form modally and returns a value for the result (if needed).