I am including a jsp inside one of my jsps as follows
<form method="post"> ......some code <%@ include file="addressFind.jsp" %> .....some more code </form>
If you are including a form within another form then you are generating invalid HTML. It has nothing to do with the include -- the same thing would happen if you didn't use the include and generated an HTML file with a form within a form.
Remember, JSP is just a templating technology to generate the HTML page to send to the browser. It's your repsonsibility to ensure that the HTML that gets generated is valid.